Why do cruising guys act like this?

There's a certain "cruising face", coupled with the typical "my body language is not sus at all" while we do the cruising thing. I know it's useful as a sign for other people who are into it to know you're also into it, but the half neutral half scared face turns me off a bit and honestly don't get it.

Why don't people engage with other people in a more friendly way? Why not smiling a bit more or having a bit more of a conversation? I mean, we are here to have fun, to be kinky together, aren't we exited? Is it fear? Is it nerves? Is this how people normally express their hornyness? Are they trying to supress their emotions or am I expecting too much?