I really don't think otaku are the problem. Pretty much as early as the 80s, you had anime that was made to cater to otaku. Granted, their tastes were generally different back then compared to now, but the fact remains that they existed and were still catered to.
My take on this, and I say this whenever the topic comes up, is pretty simple: "It's the economy, stupid". The Japanese economy is a dumpster fire, and so it's prohibitively expensive for new blood to enter the market. This means that all (well, most) of the guys with that creative spark who surely must exist somewhere in the Japanese population of today just never wind up getting the opportunity to show their stuff. The end result is a pretty homogeneous industry that caters almost *solely* to the demographic that'll shell out the most. I mean, I don't have anything concrete to back this up, but I'd be willing to bet that, although there are a large number of anime being produced today, they're mostly getting made by a relatively small number of companies.
To springboard off of what >>173946470
said, something like this has happened in the world of western cinema as well. It's just that western execs took a different approach and decided to just water everything down, the end result being movies that're so safe that they "sort of" appeal to most demographics. You used to see way more originality in Hollywood movies, just like anime used to have a bunch of imaginative OVAs covering a wide variety of styles and genres. While the start has been rocky in many respects, I'm hoping that streaming services like Netflix (not necessarily Netflix itself, although I do like Crybaby quite a bit) can remedy this somewhat.