i am not 28, but i am at a point in my life where people are no longer just free to hang out on a whim. i think it has partly to do with the fact that people are busy with their lives, and are actually focused on doing well in school/climbing the ladder at work etc. i don’t think it’s because people don’t care about spending time with you, but maybe it could be a good idea to look into ways to meet new people. making friends as an adult is literally impossible without having some activity you share, so if you’re able to, join a club or group if some kind and attempt to reach out to people there. there’s nothing wrong with trying to make new friends no matter what age you are, and the worst thing that can happen is that yall just end up being acquaintances and you get to continue and meet more people and try to make friends again.