They don't enslave well. You can train them pretty well to do specific tasks with food, and other rewards. There is an intelligence. However their "freak the fuck out," factor is a 10. For example:

https://www.cbc.ca/news/world/california-chimp-attack-leaves-man-in-critical-condition-1.562263

Domestication of animals which is the nice term for animal slaves, requires animals that are good candidates. CGP Grey has a video on this if you want to dig. Now as monkeys is a big group of primate species some are better than others, but none are really great.

This has been looked at extensively for both military and industrial application. There is certainly some use for monkey labor so to speak, but as a whole, just not that useful.