So I gave a quick look to your library just to have a rough feel for how our tastes differ, and where they're similar. From my quick glance I can guess that you and I both tend to like comics that are on the "darker" end of the spectrum, where our tastes mainly differ is that the stuff that you read tends to look more polished and (for lack of a better word) mainstream, wheras the stuff that I read tends to be a bit more "quirky". I don't mean to put words in your mouth, and this is just a surface level first-impressions sort of analysis. I'm also pretty sure that I'm younger than you are? I remember you sharing your age in another thread.
I bring all of this up because, you're right, taste is subjective, what we find good is different in some ways and similar in others, and by extension of that logic, what we find bad must differ too.
That said I feel like whats happening on webtoons is more than just a situation of "kids have bad taste". They do. I had bad taste as a kid, I'm sure you did too, I think most people do. But speaking for myself, I still had reasons for liking some of that bad stuff I was interested in as a kid, and I imagine that kids with bad taste have reasons for liking the stuff they like too. When it comes to some of the things on webtoons, I feel like there is no reason that anyone would like it at all, regardless of taste, that still gets 1000's of views, and it gets those views quickly.
I had to put my tin-foil hat back on for this response, sorry. I'm interested in seeing the results of @Im_moron 's experiment.