@Dezaki Because support classes don't generally have the ability to do stupidly badass things on their own since they're, ya'know, support classes (unless you've got some healtank sumbitch), which means they can only really shine in parties, which means a larger cast to share the limelight with. Broadly speaking, isekai stories are essentially wish fulfillment and pure escapism for overly stressed young men, so the idea is to have a teenage protagonist that they can slip into the shoes of and imagine themselves doing these super awesome things that win them a bevy of beautiful babes with little effort. Hence, you get OP protagonists that can do anything, casually pick up a harem by breathing in a world where polygamy is normal, and never really face much in the way of difficulties.
Isekai also serves the same purpose for their writers, as well, since they're most often the same target audience: stressed out, overworked young men who contribute to something like 70% of the country's suicide statistics. Who wouldn't want to escape to a world where everything's easy and you don't actually have to muster up the courage to so much as speak to a girl when they just surround you for being awesome?
@ultimatehaki The king's not sending him back immediately for the plain and simple reason that he
can't. This is just speculation, by the by, but in the
vast majority of isekai, getting summoned is a one-way trip no matter how much the MC searches for a way home; this is doubly so when it's actual reincarnation, although it wouldn't surprise me if summoning worked akin to the theories on teleportation (that is, your body is broken down, transported, and then reconstructed; sure, you're a perfect copy in every way, but in essence, you die during the process).
