There were also expectations (and I think explicit promises?) in some cases that fighting for the metropole would be rewarded with independence. So you either follow through on that (and transition to more neocolonial forms of exploitation) or balk and face resistance.

Other factors include:

1. Increasing connectedness/understanding/media exposure. It's easier to exploit some Orientalized far away peoples when you rarely see or hear about the fight; it gets harder when you have more interaction with them, you have prominent people questioning a lot of the colonial tropes that have been used as justification, and you have greater media exposure of the fighting.
2. The Nazis did a colonialism on imperial countries, which made it harder to justify doing colonialism on the imperial periphery. The British could invent concentration camps in Africa in the first part of the 20th century, but once the reality of what a concentration camp actually entails is brought home, popular support for those sorts of practices will drop.
3. Unprecedented opposition to the colonial order via aid and public criticism from the USSR, and to a lesser extent the whole project of the UN and a (weak, fleeting, but superficially radical) "commitment" to the concept of human rights.