I think it's just wish fulfillment. That thought that even the most ordinary of ppl can be someone that's undeniably special is attractive. I see it happen most with chinese webnovels where the protagonist is always the hidden child of the most powerful family that got lost for whatever reason. It's really counter intuitive since they all need to prove themselves as someone worthy to respect but then takes a shortcut and gain the respect of everyone by lineage. Complete 180, turns out you need to be born special lol
The manhuas always spice things up with more and more convoluted plots/arcs and very stupid evil jealous bitches and power hungry greedy psychotic assholes.
And what attracts them like flies to manure is the perfect beautiful powerful most desirable tsundere ML and the FL who suddenly becomes a popular Mary Sue who is slightly inferior to her man.

I ve read the spoilers about this story and I can't relate to the trope anymore that these two MCs were either reincarnations of special chosen people, former gods, children of highly valuable powerful origins/heroes/extinct race or fated lovers from past lives...
Why do the authors make the FL + ML more special and important than they already are?
Always revealing in a plot twist that their true origin is all that matters and will change/save the world...
A good example: Rey from Star Wars was supposed to be a nobody abandoned by worthless parents but then in the third movie it is revealed she is the granddaughter of Emperor Palpatine. Which means Rey is defined by her bloodline after all and not by her own strenght.