[Matrixbeast]

Word of mouth is a very fickle thing. It takes some time to get people back into watching.

As for Sentai as a whole, it's clear that while the theme for Kyoryu is back to basics, they are subverting a lot of more recent Sentai tropes. King is brash and energetic, but he's not a fireball like Ban or Jan. Hell, Nobu is older than 25, which is something that usually only occurs for members outside the core 6.
While they are playing it safe (I highly doubt we'll see them utilize Nobu's family as a possible plot outside one or two more episodes), it is nice that they're subverting the norm.

As for new themes, I think it's clear with the failure of Gobusters that sometimes they're just not up for the task. They could take theme after theme and make a new Sentai each year, but with the likes of Dinos or cars, we've seen that there's a lot more to offer by revisiting older themes with more potential.