I'm not sure I fully understand the idea behind this topic so I probably might wonder off-topic. But still. Anime has turned seasonal since forever (or at the very least 2008-2010) which is a good thing because in the prior age it has been plagued with anime original endings and other god awful mockery of the source. On the other side, anime is now a lot less standalone and self-contained, often feels like a short promotion.
But it's not like it's something new, the current generation possibly doesn't even remember those times...? And not much has changed since the shift, except maybe the introduction of split-cours and seasons becoming shorter and shorter.
Maybe for some it feels like the seasons have become more frequent and hence more "seasonal" but in reality it's really just Shounen Jump. While they did more long-running series before, nowadays they usually prefer to test the waters first and then continue with the more popular franchises. Plus they are now giving at least one season to literally any relatively popular manga.
Others are pretty much doing the same thing they have always done though. Unfortunately, I don't feel like there are all that more sequels than before, just the usual super-popular things, the rest stops at two seasons at best. Often it's pseudo "two" seasons when they cut a planned 24-episode series into 2 seasons of 12 eps. And as always the best stuff usually has only one >_>
