Why is so hard to make friends as an adult?

I've never been the outgoing type but after graduating and having left my school friends behind I've been having a really hard time meeting new people.<br>Everybody seems to be doing it for themselves or they all have their own friend group from school that I'll never be able to penetrate. I've tried joining clubs but they're full of kids.<br>I've recently moved to a new city (1.5 years ago) so I'm hopeful one day I'll meet people but it's hard to bear.<br>I've tried so many things, classes, gym, bars, coffee shops, courses, Tinder, you name it.<br>I'm not that socially inept but it's harder than ever.<br><br>Edit: Thank you so much to everyone who's commented so far, it's reassuring to know I'm not alone and there's light at the end of the tunnel. Thank you for some really good advice too.