Answer:
There are actually a few good reasons but there are 3 main ones, i call them the 3 Main G's which mean God, Gold, and Glory.
Explanation:
Colonizers would colonize other people or land for greed, power and labor, Back when America was still the British colonies, The more land you owned, the more power you had and more slaves to work that land.
Theres also times when others colonized people to teach them a certain religion.
Some just colonize for the glory of it or for the land's natural resources
I hope this helps