I think it's because of the business scheme of the anime industry in Japan, products that have a lot of fanbase beforehand or that are sure to sell, don't make an effort to give a lot of animation except perhaps in specific moments or movies, for that Dragon Ball, despite selling so much, brings out something outstanding in animation. Now new series that are only going to sell one season and it's all or nothing (like most of Slice of Life or moe that are only successful for one season and that's it) take out the animation ceiling to attract attention. Of course there are exceptions like Kimetsu no Yaiba that I understand was because a executive from UFOTABLE liked the manga and wanted to be encouraged by the animation top, and then he was lucky that it was a very profitable success.
