Why are the Japanese people incapable of keeping a good story going past the first season?

Made in Abyss season 2 was such a massive drop in quality from the first season, with an nonsensical plotline and absolutely dogshit character development, it makes me think that the first season was just a fluke

and it isn't just made in abyss either...
promised neverland
one punch man
ranking of kings
etc

every single time there is an anime where the first season rocks they drop the ball so hard in the next you have to wonder what the fuck went wrong