The way I understand it, they handle money and regulations, i.e. collecting money from the player, giving the player actual money back when the player wins, in

The way I understand it, they handle money and regulations, i.e. collecting money from the player, giving the player actual money back when the player wins, in a way that is 100% legal considering gambling laws in all countries involved in each transaction. That's a lot of stuff for a regular developer to take care of. The part where they also run the gambling logic & randomness is probably necessary because regulations on gambling often require certain guarantees and auditability that, again, a regular developer may not (want to) be aware of. It's much simpler to be compliant if the dev only has to establish f.ex. win rates for different actions, and the gambling provider runs the actual processes with methods and random generators that comply with applicable laws.