Which sites? Most sites that allow posting/liking/commenting on anything require that you sign up, including all social media sites.
Yes? I'm sorry, I don't understand what's unusual about this. If you want someone to spend their time/money/effort promoting you, you either have to have an existing following, or you have to be GOOD, just like any time you submit to a slush pile. Tapas is not lacking in talented and/or successful creators offering up their work for the writers camps and incubator and such, if you want to compete in that arena you gotta fight long and hard for it.
If it's curated by staff, that's the same as New And Noteworthy. If it's an algorithm, it's just trending minus the big guns. But trending is already pretty fair, I see smaller series on there all the time. And in either case you're still putting an arbitrary number on what does or doesn't deserve the bump.
I'm all for creators having more chances for visibility, but I still maintain that better searching/tagging is a much higher priority in that regard, tbh.