Why does Christianity have so many denominations?

Christianity does not have any denominations per se. Only religious organizations, cults, sects, and pseudo religions form various denominations.

For the same reason that Islam has 57 different sects within the Muslim faith. The Shiites and Sunnis are the most visible, but there are many many others, and they all follow the Qur'an to differing degrees. 

Because a lot of people have to get their fingers in the money pie.

That kind of sums it all up doesn't it.  If there truly were a deity then there would be only ONE deity.  There would be only ONE holy book written by that deity.  Everyone on the planet would understand it without question.  Everyone on the planet would worship that ONE deity.  Everyone on the planet would understand that holy book without the ridiculous need for interpretation of it.

Because the church leaders are all looking for a place at the money table and they invent another version.  This is absolute proof that it is, in all of the versions, a totally made up game. If there really was a true version there would be only that one, but money plays a huge role in religions, as Christianity re the NT was written and started by the Romans for political reason. A lie can be twisted and used in many different ways, and that is Christianity.

Because different people like to make different stuff up. 

People do not want the truth, but they want their ears tickled.

When you ask a person, 'why do you attend the church you do?'

They will most likely answer:  "I just love the minister"

(2 Timothy 4:3, 4) “3 For there will be a period of time when they will not put up with the wholesome teaching, but according to their own desires, they will surround themselves with teachers to have their ears tickled. 4 They will turn away from listening to the truth and give attention to false stories.”

This separation started during the time of the apostles and continues to this day.

(1 Corinthians 1:10-13) “10 Now I urge you, brothers, through the name of our Lord Jesus Christ, that you should all speak in agreement and that there should be no divisions among you, but that you may be completely united in the same mind and in the same line of thought. 11 For some from the house of Chloʹe have informed me regarding you, my brothers, that there are dissensions among you. 12 What I mean is this, that each one of you says: “I belong to Paul,” “But I to A·polʹlos,” “But I to Ceʹphas,” “But I to Christ.” 13 Is the Christ divided? . . .”

This separation is because people want to decide for themselves what is right and what is wrong or as one commenter said:

"truth is found only in the individual mind."

All who claim to be Christians must take on the mind of Christ, which will remove all the divisions found in the world today.

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Because after the death of the apostles, Christianity went apostate, In fact the apostles said while they were still alive that it was already starting. In the Book of Daniel, God said in the end truth would be re-established.

truth is found only in the individual mind.

Correction - Protestantism has so many denominations - over 6,000 of them at last count - all created within the past few hundred years, each claiming to get their 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, which are just mini-denominations. Exactly the opposite of the clearly stated will of Jesus Christ concerning His followers, which was and still is "That they all may be ONE, even as I and My heavenly Father are ONE". He knew that truth can exist only in unity, because truth cannot contradict truth, and contradictory beliefs therefore always mean false beliefs. Meanwhile, the ONE Church Jesus Christ founded (which includes well over half of all Christians) remains ONE in belief, ONE in teaching, ONE in worship, ONE in biblical understanding throughout the world after 2,000 years, with NO conflicting denominations, just as He intended.