Mostly because all land is claimed by some country or another, and the current occupants could raise enough of an international stink that people come to their defense.

One might argue that what Russia is doing in Ukraine and Georgia is the modern equivalent of colonialism.

There may be other reasons, but morality is unlikely to be one of them.

I mean the British had a huge role in ending slavery, not because it was the right thing to do but because other countries were doing it better and so it was better to invest in stopping others than doing it themselves

The US and USSR similarly ended most colonialism because they were the most powerful nations in the world and yet couldn't compete in that field

As countries become powerful, they seek to destroy whatever the previous symbol of power was and replace it with whatever they're good at until the next newly powerful country comes along

There are a few obvious wrinkles in his plans. Poland, for example, is probably the most significant European country without a past as a colonial power in Africa, Asia or South America but politicians from around the world will not be blind to some of Warsaw’s latest pronouncements on migration. Polish Prime Minister Mateusz Morawiecki recently said he wants to hold a referendum asking citizens whether they support the arrival of “thousands of illegal migrants coming from the Middle East and Africa.”

So which European country that isn't racist and doesn't have a colonial past?