Because some of them will be cool people and you will benefit from a world in which they are happy and make amazing things. This is true for basically everyone. If the distinguishing feature of the group is not “actively harming other people”, then caring about the group is useful.
Furthermore, everyone benefits from a society in which there are not special unprotected classes who do not enjoy basic civil rights, safety, etcetera. Because if there are such classes, everyone could potentially end up categorized as being in one of them. Not everyone beaten to death for “being gay” was actually gay!
That, and… If you want the 100% pure self-interest answer, in general, the correct answer is “the best strategy will be to consistently, persistently, and at multiple levels of motivation and decision-making, act as though you have goals other than 100% self-interest”. If the perception that you are motivated by 100% self-interest is every anything but a theoretical pure abstraction that obviously has nothing to do with how you behave, or your long-term goals as inferred from your actions and statements, you will probably be fucked over really badly by this. Because it is absolutely in everyone else’s best interests that (most) people who are motivated by 100% pure self-interest are fucked over as much as possible at all times, because any power they get will consistently harm other people.
So if you want to be happy and successful, care about other people, and oppose marginalization of humans at all times and with significant energy.
just moving along like everyone else 