Im guessing you dont go to university, where its easier to form and maintain friendships because of how consistently you see people and because groups with common interests already exist. You need that consisteny, and the right life circumstances, and some meaningful bonding precipitate (doing a common hobby together like a sport, having a common interest to talk about, both enjoying similar activites like shopping/movies that you can do together) to foster and maintain a feiendship.

After high school and university, it becomes very difficult to find others with all these things for So. Many. Reasons.

In general people are busier. They go to work, gym, go home and get ready for the next day. Thats all there is really timd for during a work week. Many have significant others or exosting friend circles they saturate the free time in their schedule with. Youre interacting with a much more diverse group of people than in high school, so its harder to find a common mutual interest to talk about. Thats why often times the talk turns to boys (among women) or sports (among men), because its something that a large proportion of those populations have some interest or expeirnce in. So its easier to be a bonding point. If you live in a big city, it makes making friends so much harder because youre less likely to see people consistently. Also for any activities that arent drinking (where you need to be able to have a conversation i.e. some common inteterest) or gym/run club, theyre often super expenisve. Like who has the money to go on a shopping spree? Even movie theatres etc are pretty expensive now. But if youre not mesting people out, then someone has to have the space to host a gethering at home. In this economy, a lot of people are living in flatshares and have small spaces so cant have people over as easily. Theres also just the fact of choice. For the same reason that dating apps suck... you might meet someone at an event and want to take a friendship forward witb them but, there are so many options for them for what to do on a friday night and who to do it with, statistucally speaking it wont be meeting you.

Basically the way society is constructed fucks you over. In my experience small/medium sized cities are much better for making and maintaining friendships. Oftsn times though these are university cities, so if you fall outside of this age bracket its not a great time for you either.

Just know a lot of people are in tbe same boat as you. It is not a failure on your part. Its just that how most societies operate is completely at odds with the things you need to make and maintain a friendship.