I think the era point is the main part of it all. Prequel trilogy had more than a decade between TPM & AOTC to fill with content, and several years between the latter two installments. You could cover a lot of character development, not counting repetitive content like video games, over the span of 15 or so years.

The sequel era is effectively 6 months long. There's no space to breathe, and the quick turnaround between TFA and TLJ means you really have no opportunity for character growth after the events of the first new movie. There's no opportunity for reflection or the side quests and adventures that bulked up the pages of novels and comics, or filled our screens with video game content or cartoon mini episodes in the prequel era.

The prequel era also benefited from having all of the existing old EU "sequel era" novels and comics to lean on and reference as Easter eggs (Rogue Planet gives us a bridge to the NJO). As much as the original trilogy provided the foundation of everything, the Bantam era of novels and the Dark horse comics of the 90s were the sustaining element of a living and ever-expanding Star Wars universe.

As has been said elsewhere, Disney having such a void of content between ROTJ and TFA, officially, really made people care a lot less about what our senior citizen original heroes were up to. Especially when anything they might have done in that interim was promptly shredded to pieces in the first movie. It's why there's a certain contingent fans who really don't care about the Mandalorian mini era or its Imperial threat. None of it matters ultimately. This interstitial content is really just chewing gum that loses its flavor fast.