Why is the eleventh month of the year is called November?

The names of the months originated from Old English or Latin
Originally there were only 10 months in a year
but Julius Caesar added two months -- July and August before September
so if you count back, the November today is the 11th month, but it was the 9th month in the past.
"nove" is the Latin word for number 9
that was why the original 9th month is called November
only that nowadays, November has become the 11th month of the year

November is the eleventh and penultimate month of the year in the Gregorian Calendar and one of four Gregorian months with the length of 30 days.

November begins in western tropical astrology with the sun in the sign of Scorpio (astrology) and ends in the sign of Sagittarius (astrology). Astronomically speaking, the sun actually begins in the constellation of Libra, passes through Scorpius from approximately the 24th through the 29th and ends in the constellation of Ophiuchus, which is the only zodiacal constellation that is not associated with an astrological sign.

In Latin, novem means "nine". November was also the ninth month in the Roman calendar until a monthless winter period was divided between January and February.

In old Japanese calendar, the month is called Shimo tsuki (霜月).