Everyone brings up so many great points! Interesting perspectives to read through (also Qia your new avatar is so cute!). 

I won't repeat much of what everyone else already said, but I do want to bring up something very important to me when I read interest checks or RPs. My tastes are generally diverse (though lately been leaning more in certain directions), so a lot of things catch my attention... but what makes me more likely to keep going back to an int check or RP and apply to it is how invested the GM is in their own story. This can translate to making a lot of cool aesthetics for it, doing detailed world building, or just how enthusiastic they seem when talking to potential players. If the GM seems really into their own idea, especially to the point that they wouldn't get discouraged over hiatuses, slow posting, or players dropping, I think it's more interesting to their audience too. And you can definitely tell a person's investment into a story from their writing and behavior.

This goes for players too if its an already established RP, general enthusiasm goes a long way for me. On the flip side, if there's already a cast of very invested people even at the interest check stage then a lot of the times I let them be and just read along instead of trying to squeeze in. Reading along is pretty fun though so no complaints from me lol.