I'm definitely not disagreeing that manga can be more interesting. I'm mainly a manga reader myself, and find many more interesting series covering esoteric topics. But it's about appealing to the largest possible audience, and the reality (and I say this once again based on my and other's stats) is that
currently, the male audience wants some variation of the escapist video game or medieval Europe setting with the weak-to-overpowered protagonist using swords and sorcery, probably reincarnated or time-traveling from the life of a loser/weakling. The female audience wants a medieval Europe setting where the protagonist (probably originally an average-looking female in our world or theirs) is either a "villainess", maid, knight or someone other position that makes is possible to have a reverse harem of hot guys with a sadistic or cold-to-warm (tsundere) personality. Those setups are being endlessly mined for new series, just adjust the variables and bam, new series.
I do think that there are also some unique webtoons out there, you're just going to have trouble finding them because they're buried beneath the huge pile of more widespread popular series, which is what all the artists with talent are focusing on (Korean webtoon studios, and the industry as a whole, is a lot more profit-driven). It's also easy to judge a webtoon by its cover and think "oh yet another OP protagonist". Try some out, maybe you'll like one!