if God loves us so much like the Christians claim?

Read the first three chapters of the Bible for full disclosure. 

God placed Adam and Eve in Eden, heaven on earth. Perfect wasnt good enough for Adam so he betrayed God, who then ejected Adam and Eve out of Eden and into a cold, hard, relentless world ruled over by death and decay. 

Because forces opposed to God’s will have a hand in the game.

God's love has already been demonstrated to a superlative degree, so that no reasonable person can doubt it. He gave us the best that He had, to remedy our cycle of sin, suffering and death. Only what God freely gave us can deal with all that we suffer from in this mortal existence. God is waiting for us to gladly accept that gift and to run with it, into an existence where we have been liberated from the sin that causes suffering and death.

That won't stop anybody suffering at the hands of humans who continue to sin and to be selfish; this side of eternity we all "reap what we sow" and if others sow hatred and war etc, we will reap that evil harvest along with everyone else. But God has already shown us a better way, and we need not be bound by the misery of sickness and death. He can enable us not merely to cope, but to help others and so pass on His love.

Because we live in a natural world and are therefore subject to the laws of nature, just as Jesus was when He lived on Earth. He offers us an eternity of prefect happiness in Heaven. We can't expect perfect happiness on Earth as well.

As William Lane Craig argues, God has morally sufficient reasons for permitting suffering. God wanted to create a world of free creatures who could become responsible moral agents and mature persons. The goal of life is not happiness in this life. We are not God’s pets. It was not His goal to create a nice terrarium here for His human pets. God’s purpose was not to make life easy, but to make man great.

Suffering and difficulties can help humans develop some of the most treasured traits known to mankind like bravery, heroism, altruistic love, patience, self-control, self-sacrifice, and others like that. There are certain qualities that we simply cannot acquire in the absence of hardship and suffering.

In the movie, Shadowlands, C. S. Lewis asked, “Does God want us to suffer? What if the answer to that question is ‘yes’? You see, I don’t think that God particularly wants us to be happy. I think He wants us to love and be loved. He wants us to grow up.” And he would say that suffering is the chisel by which God perfects us: “We are like blocks of stone from which the Sculptor carves a form. The blows of His chisel which hurt us so much are what makes us perfect.” 

As the saying goes: “What doesn’t kill us, makes us stronger.” And God wants us to be strong. Difficult training makes the athlete faster, stronger, and more skillful. Each battle you go through makes you more seasoned. When seen from the Bible’s viewpoint and perspective, suffering is often a good thing that is preparing us for eternity. As the Psalmist said, “It is good for me that I was afflicted, that I may learn Thy statutes” (Ps. 119:71).

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Why do we suffer (according to the Bible)? 
-Our own actions (Proverbs 23:29-30; 1 Peter 2:20; 4:15) 
-Other's actions (2 Samuel 4:4; Luke 13:1-3; 2 Timothy 3:12) 
-Training and discipline (Deuteronomy 8:3; 2 Corinthians 12:7-10; Hebrews 12:4-11) 
-To test our genuineness (Deuteronomy 8:2; James 1:12; 1 Peter. 1:6-7) 
-Sometimes we cannot know the reason (Job 40:1-4; John 9:1-3; Romans 8:28).

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God and Suffering
https://www.youtube.com/watch?v=cNtz5wgnopQ

How could an all-powerful, all-loving God allow evil to exist?
https://www.youtube.com/watch?v=NAm8iK8VhV0 

This article answers your question: https://www.jw.org/finder?wtlocale=E&docid=502018850&srcid=share

The Bible emphatically answers no! Suffering was not part of Jehovah God’s purpose for mankind. However, the first human couple rebelled against God’s rulership, choosing to set their own standards of good and bad. They turned away from God and suffered the consequences.Today we are experiencing the effects of their bad choice. But in no way did God originate human suffering.The Bible says: “When under trial, let no one say: ‘I am being tried by God.’ For with evil things God cannot be tried nor does he himself try anyone.” (James 1:13) Suffering can afflict anyone—even those who are favored by God.

Because we don't love Him

love is a gift that must be accepted, otherwise you are on your own

Why do people love their sin and prefer that to God, and then complain of COVID-19, cancer, autism, and many more diseases??????

Why aren't they happy with their choice?

That's the problem of evil, for which they have nothing but lame, unconvincing excuses.