Guys looking at me but don’t make a move or talk…

I’ve been in such situations before where I had either chemistry or visual chemistry, or some sort of interest or comfort with the person, but never really happened anything with anyone.
First either they were curious, or found me cute and nice, like guys in the gym, or in the university, now by looking I mean, actually just looking at me whenever I’m around…
Second, I later found out through social media or their friends, that they have gf’s or are taken or unavailable, or don’t like me like that.
And by experience now, I’ve learned not to take a guy seriously when he looks at you, whether or not he makes moves on you. I don’t take the guys seriously who makes moves on me because I don’t trust them, but it’s especially with guys who just looking and don’t do anything about it.
It makes me feel like I’m some sort of a thing to just look at but not to be treated right or made efforts for.
Now I’m not talking about just anyone and everyone or random guys out there.
I’m talking about these specific guys (who I like as well), who would do things to get my attention, but not come up and talk to me. Or the ones who just look when I pass by, but not do anything about it.
It’s so annoying and idk what to do about it. When I try to make the smallest talk, I get a bland answer, and I just assume that oh then he must just have a girl and he looks bcuz he’s nice or maybe he doesn’t look and I’m just paranoid lol