Why do non-Catholic denominations of Christianity exist considering that the Catholic Church was the one & only that JesusChrist established?

Considering that you're wrong, you have no question.

The Christian Church was founded at Pentecost when the Holy Spirit descended in the form of tongues of fire over the heads of the apostles, changing them from scared mice into fearless evangelists.

The Christian Church was one till the Great Schism of 1054, when it split into the Eastern Orthodox Christian Church and the Catholic Church.

Because prove it.

The truth is, the Roman Catholic Church didn't exist until the year 1054, when the original church split into two factions.

The Catholic church came into exist in 1095 when it broke from the Orthodox church.  If Jesus established that church wait 1095 years to do it?  That is half way through the current history of the Christian church.  

Your Premise is untrue, the Christian Church existed 450 prior to the Roman catholic church

The Catholic Church suffered from infighting for a thousand years before the Reformation splintered it into Several new Sects...
It wasn't about beliefs and Dogma, it was all about money...  
The 35,000 or so Christian Denominations have 35,000 or so different bank accounts...   

There is still big money in Jesus  

Because of one misguided man who thought He could do a better job of interpreting the Bible, than the Church that compiled the Bible under the guidance of the Holy Spirit. Luther defected from God's Church and founded his own church, based on "the Bible alone", which obviously meant his own interpretations of the Bible. Before he died there were half a dozen other Protestant denominations that had broken away from Luther's church because they didn't agree with his interpretations. The doctrinal chaos of Protestantism had begun. Today, a few hundred years later, there are over 6,000 registered Protestant denominations, each one claiming to be teaching from "the Bible alone", yet the teaching of each one contradicting the teaching of the others. And that doesn't even include the 20,000+ so-called "non-denominational" Protestant churches. Exactly the opposite of the will of Jesus Christ for His followers, which was and still is "That they all may be ONE, even as I and My heavenly Father are ONE.

Here the answer: https://www.jw.org/finder?wtlocale=E&docid=502015171&srcid=share

PLEASE READ>>>

 IF YOU WERE TO LOOK INTO IT VERY CAREFULLY, YOU WILL LEARN, THAT THE ROMAN CATHOLIC CHURCH IS THE ONLY ONE JESUS(GOD INCARNATE) STARTED, IT IS 2000 YEARS OLD ALL THE PROTESTANT CHURCHES ARE AT MOST 500 YEARS OLD. JESUS GAVE HIS CATHOLIC CHURCH THE SEVEN SACRAMENTS OF HIS CHURCH EVEN BEFORE THE BIBLE WAS FIRST FORMED BY HIS CHURCH. NO ONE HAD THE BIBLE BEFORE THE CATHOLIC CHURCH FORMED IT. HIS CHURCH IS A PACKED GOD MAN WITH IT THAT WILL LAST FOREVER. SEE HERE FACTS AND ESPECIALLY THE LINKS, PLEASE READ ALL>>>>>>>>>>>>

  JESUS SAID TO PETER, PETER YOU ARE MY ROCK, ON WHICH I WILL BUILD MY CHURCH(UNIVERSAL)(ROMAN CATHOLIC) AND THE GATES OF HELL SHALL NOT PREVAIL AGAINST IT. THE SACRAMENTS OF THE CATHOLIC CHURCH WERE INTRODUCED BY JESUS HIMSELF(CONFESSION, WHAT SINS YOU FORGIVEN ON EARTH, THEY ARE FORGIVEN) NOW, HOLY COMMUNION(JESUS BROKE BREAD AND SAID THIS IS MY BODY WHICH WILL BE GIVEN UP FOR YOU, THEN THE WINE, THIS IS MY BLOOD WHICH WILL BE POURED OUT FOR THE FORGIVENESS OF SINS. DO THIS IN MEMORY OF ME. AND NOW BAPTISM, WHICH IS THE TRUE BORN AGAIN MEANING, AND THE MEANING THAT GOD IS THE TRINITY. WHEN JESUS SAID YOU MUST BE BAPTIZED WITH WATER, AND IT MUST BE IN THE "NAME OF THE FATHER, THE SON, AND THE HOLY SPIRIT. IF NOT DONE THIS WAY, IT MUST BE DONE OVER, THIS IS JESUS'S WORDS, NOT MINE.
SO YOU SEE PETER WAS THE FIRST POPE(EVEN THOUGH THEY DID NOT USED THE WORD POPE AT THAT TIME) AND JESUS INTRODUCED THE SACRAMENTS OF HIS CHURCH, EVEN BEFORE THE BIBLE WAS FORMED BY HIS ROMAN CATHOLIC CHURCH, NO ONE HAD THE CHRISTIAN BIBLE BEFORE THE CATHOLICS AND THEY WERE THE FIRST CHRISTIANS EVER..
SEE HERE FACTS>>>

THE ONLY CHURCH STARTED BY JESUS HIMSELF WAS THE ROMAN CATHOLIC CHURCH AND THEY ARE THE FIRST CHRISTIANS EVER AND THE GATES OF HELL SHALL NOT PREVAIL AGAINST IT, SEE WHY OTHERS RELIGIONS SPRANG UP AFTERWARDS>>


 BUT IF THEY DONT WANT TO LISTEN TO JESUS AND HIS CHURCH, THEN HE WILL NOT INTERFERE WITH YOUR FREE WILL, WHEN JESUS STARTED HIS ROMAN CATHOLIC CHURCH IT WAS ONE CHRISTIAN CHURCH, BUT GOD KNOWING MAN LET THIS HAPPEN AND THATS WHY THERE ARE SO MANY PROTESTANT DENOMINATIONS, >>>

 MARTIN LUTHER A CATHOLIC PRIEST
DECIDED HE DID NOT AGREE WITH ALL THE TEACHINGS AND
BECAME A HERETIC AND WAS EXCOMMUNICATED FROM THE
CATHOLIC CHURCH, HENCE 39,000 PROTESTANT DENOMINATIONS. SEE HERE WHERE ALL CHRISTIANS WERE
CATHOLIC AT FIRST AND ALSO HAVE THE ONLY TRUE BIBLE >>>>>>>

    The ONLY Christian church in existence for the first 1,000 years of Christian history was the Roman Catholic Church. All other Christian churches which exist today can trace their linage back to the Roman Catholic Church. Most non-Catholic churches which exist today are less than a century or two old by comparison. ALSO TRUE BIBLE READ>>>

The Catholic Church is entirely responsible for the composition of the Bible, which books are included, as well as the breakup of the chapters and verses. Protestants have removed some books of the Bible because some of the verses were inconsistent with their theology. Martin Luther was a prime offender in this regard, removing Tobit, Judith, 1 and 2 Maccabees, Wisdom, Sirach and Baruch. He also made an effort to remove James and Revelations, but this was rejected by his followers and those two books were kept. Catholics are often accused of "adding" the books, but despite this common belief, it is false. Older, pre-Protestant, Catholic translations of the Bible include them.

NOTE, WHO FOUNDED YOUR CHURCH, CHRIST OR MAN, SEE HERE AND BELIEVE>>>>

https://www.youtube.com/watch?v=N44R4rgrR58

Only if you twist the words of the Christ for your political purposes

DIDN'T FOUND A NEW RELIGION:
The Roman Government used Theophilus, Luke, and Paul, to establish the COUNTERFEIT church of Paulism/Romanism which later became Catholicism and other denominations. The REAL APOSTLES' involvement is mostly fabricated by Luke.