[Byg42]

While that does get into how Hasbro buyout of Power Rangers affected the commercial aspect of Sentai, I think this interview with Shirakura shines light on the creative issues that Sentai has been having.
https://archive.ph/N1ZcY

Basically, Sentai sheer longevity has caused issues in the creative process and on its popularity. The advent of streaming meant new Sentai shows were competing with older shows for attention. It's long presence on air and the somewhat unchanging nature of Sentai meant older viewers felt little reason to watch newer shows, as to them it was just the same. Sentai also became stuck in following its own formula rather than thinking what would be best for the show, recalling that even as early as Zyuranger, the first conversion of production was "how do we do the giant fights" rather than "what is this show about". With all this, I get the desire to put Sentai on pause for now, to give it a creative reset and figure out how it should be handled in the future