In general, my experience (and the experience of various friends) has more been that you'll have established a relationship (meaning "You're not strangers", not the romantic kind) over a few weeks, and conversation is going smoothly, and then it just... stops. And I don't mean "I took a chance saying something risky and she never replied". A back-and-forth conversation that'd been going for weeks just suddenly stops going without any real change in content.

I.E: I'd been talking with a girl for a month or so, and we'd hung out a few times. One night she says she wants to invite me over to watch a movie she'd brought up earlier but was busy that night. I reply that that was fine, I was busy too, but that sounded fun so maybe we could find a time later in the week. I didn't hear from her all that weekend (I also didn't reach out). She sent me a text early the next week about something random, but it was all short 2-word replies from there on, so I moved on.

Obviously it isn't worth getting hung up on. It's just confounding when it seems to happen with some regularity to multiple people. Given the way society views dating, it's easy to think the problem lies with you - you said/did something wrong. You'd like to fix it, but you have no idea what you did. This is true even in cases where you actually didn't do anything wrong, it just didn't work out. That can be deflating, as OP mentioned.