Why is making friends as adult so hard?

I (22F) don't have a single friend and it's been bothering me for years. I didn't make any friends during college because the school I went to was more for adult learners and distance education (not a traditional university experience). The girls I worked with at my part time job were kinda my friends, but as soon as I quit we stopped talking. I travel with a travel group about once a year and some of the people I've met keep in touch on a monthly basis but obviously they live states away so not really a true friendship. I have been on bumble bff for 2 years now and haven't made a single friend from it. I've met countless people, but only hung out with about six and they don't talk to me unless I'm asking them to go do something. Nobody follows up with me unless I reach out first. Now that I'm in between jobs, I go months without speaking to a single person outside of my mom. Idk what I'm doing wrong. I've joined Facebook groups for things im interested in, did group activities, etc. but it leads nowhere. Advice desperately needed.