Abolished? Or rather optimized? Slavery was just an economical outdated method of production. Like why we don’t smelter iron in clay furnaces anymore. Also enslaved peoples weren’t consumers, since capital requires more markets, it was beneficiary to make them into consumers.
Enslaved people are also too hard to control. The best form of control is where the person controlled thinks they are free.
For sure they supported some latent ustasha remnants.