I've heard a variety of takes on this. Unfortunately the reasons (whether true or not), seem to support the results.
Rogue One Literally had no recognizable characters from previous films aside from a couple short scenes with Vader, CG Tarkin, and one scene with CG Leia. However the movie was fairly well received. I know some opinions were mixed, but personally I really liked Rogue One. For all my rantings about Disney eliminating the EU. Rogue One was , essentially, the perfect EU novel realized in film format. AND it made 1 Billion WW.
TLJ made 1.3 Billion, but still was obviously divisive, and I hate to say it, and as much as most people want to deny it, you have to think that a portion of Solo's less than stellar performance is directly tied to fallout from TLJ. I mean I wish we could live in an alternate dimension where Solo came out before TLJ, and see the box office improve, but unfortunately we cant do that. I still think that pushing the release to December might have helped a little, but who knows.
All I do know is that the argument that "If a spinoff film about one of the most popular characters (Han Solo) doesn't get people to theaters, what chance does Boba Fett, or Obi-Wan have?" Holds no weight with me, when in 2016 we had a spinoff film with arguably NO previously known characters be extremely successful.
There are no more good TV Shows, only ones that haven't disappointed me yet.