And what is the problem with doing that? The system comes back up when you reopen the lid nearly instantly anyways?

This assumes that you don't have stuff you would rather leave running in the background. Like compiling, or keeping an ssh session alive.

I at least sometimes see coworkers walking around with open laptops, which looks inconcenient. I am sure they have their reason for not closing the lid.

It does, but it still requires unlocking the session on resume, which is a minor inconvenience if you're just moving to a neighbouring room with a coffee cup in your other hand. Slightly more importantly, sometimes it's also convenient to keep network connections open, e.g. for ssh sessions.

Those aren't really problems, but it can be a minor matter of convenience, and I've set both my work and personal laptops to not suspend when the lid is closed.

I'm not saying that's in any way a better idea than keeping the typical default, and I have absolutely no opinion on what anybody else should do.

FWIW, I also don't care whether macOS gives an option for not triggering sleep when closing the lid, which was the original matter. But I don't agree that there's no reason to close the lid except for suspending.