@kkaces It should be noted that web novels are closer to "fan fiction" so you should take those with a grain of salt. Any person in Japan can write them. Also, a lot of those Isekai novels happened over a period of time.
And they are usually done by the same few magazines in the case of manga... it just feels less niche because we get it all on the website at once in a single source. But if you think about it, there is more of non-isekai... it's like getting content from a specialty magazine pushed into a general website and seeing it all the time because of it.
That said, we need to remember, these stories got popular as web novels before they were published.... so that means customers actually wanted that series... so maybe our complaints aren't fully fair... these are stories people wanted to be made into a manga.... and it was made for them....
So should we really complain about other people's tastes?