@Touje Well, yeah totally agree, like Sturgeon's adage.
But I actually do like indulging in less-than-stellar manga. It allows me to either think or not think at all, depending on my mood. I guess the interesting thing about trash isekai's specifically would be...how blatant the setting revolves around wish fulfillment and power fantasies. I know most fiction could be seen that way, and each genre has its clichés. But there's a peculiar, almost standardized way that crappy isekais go like:
"We have this useless asocial NEET/unlucky mediocre salaryman that gets transported to another world with cheat abilities and/or specialized knowledge and/or regular common sense from a modern society, which makes him a renowned warrior, a technological guru and/or a master politician. He (usually he) gathers many trusted companions, love interests, and political allies and overcome the ultimate evil and/or the petty, ignorant and prejudiced social system and the agents that uphold it. Also, slavery is sort of a thing here (without really understanding why) so just roll with it, maybe get yourself a cute waifu".
And then we have waves of isekais where the MC was either the most blessed existence and played it straight, the one where its lampshaded but still played straight ("Cheat"), the unlucky one with crappy attributes but ingenuity and awareness of the loopholes; and very few that either deconstruct it, examine it closely and add in-universe logic to how and why things are, or relentlessly parody it.
And for me it's just plain fun to see how within that 90% they add small flourishes, change a little thing and it's still pretty much the same. In the end it comes down whether I like the art or not. And also that wish fulfillment thing, because honestly it's still there.