It's probably part of it, but there's definitely also other stuff like the fact that human breasts are always prominent, unlike most other animals where the sexual display stuff waxes and wanes with them being fertile.

The best hypothesis i'm aware of is that human sexuality is just really strange and kinda.. slutty.. (this applies to everyone). Like it seems that our default way of going about things before civilization fucked it up was to just kinda have fun with anyone who caught our fancy and reciprocated the feelings, so our dicks evolved to scoop out sperm and tits evolved to always be on display so no one can tell if you're fertile or not, and presumably same thing with us having no mating season to speak of.

Just try to be attractive so as many people as possible will want to bang you, and maybe if you're lucky you can even find someone who likes you enough that they actively avoid banging others, which is pretty damn sweet because you know that kid will be yours. But in the end it doesn't really matter whose kid is whose, because everyone will help raise them.