While the cliche is a bit too repetitive it makes sense why its so used. And we see it used in shoujo manga too. It makes the relationship more special and for the characters to work hard to make it happen. Like you actually need to be a good storyteller to make a romcom story with two average people seem interesting and make it last more than 30 chapters.
Also most mangas have the mc be the underdog, its super rare to see a mc who starts at the very top. Also this status disparity introduces some drama thats not too heavy. A normal romance between 2 normal people with 2 normal lives is actually just a normal story that doesn't attract any attention.
So yeah, the fl/ml is popular/rich is a easy trope to use and is confirmed to get readers.
While I understand what you're saying and I even like a number of romcoms with this trope I still think it's a lazy troupe
There's a couple of romance manga i can think of off the top of my head that don't have the male/female lead be popular and still get traction/attention from readers
It's a popular troupe but mangaka don't have to use it
I think it's just a way for them to take the easy way out by saying someone's interesting without actually making them interesting
They just don't put in the effort to make a love interest admirable/desirable to the mc beyond superficial stuff like social status
You can also make the a male/female lead hard to get without them being fawned over by every npc in the story
Value can be perceived without a social hierarchy being involved
Even one person getting in the way of someone's relationship can cause simple drama
I ain't a writer so i can't say it's easy but isn't the goal of writing to at least improve upon pre-established troupes and creating unique characters instead of copy/pasting troupes/character traits from other series