there's a lot of different reasons yknow, but the main one would be the fact that tons of women don't orgasm so they're just doing it for their partner. which is the main sentiment from the others in this thread. for reasons outside of that, it can be to get the man more excited than he would've been had they just jumped straight into it. it's like foreplay i guess. it could also be to make sure it's wet enough. some women don't struggle with getting excited and don't need lube, but some women might need the assistance but don't wanna ask for it for whatever reason. it could probably be a power thing as well depending on the type of relationship the man and the woman has. some women like the feeling of somebody having power over them, some don't. in the cases which they don't, it could also be a sense of control. they do thing that makes their partner excited and enjoy seeing their reaction or playing into it, etc. there's like a thousand different reasons-- all different for every woman and every relationship.
tl;dr - idc don't read it i'm not gonna summarize it for yall becuz it's more complicated than a few sentences