It's not that big budget/shiny SFX space opera is out of the question, it's that big budget/shiny SFX space opera that doesn't bring in the ratings to justify its cost isn't very attractive to many tv studios/networks. It really never was.
As a rule of thumb, space opera has always been very expensive and difficult to produce, even before TOS. When Roddenberry initially shopped around TOS, he was told no several times before someone defied conventional industry wisdom and said yes. That really hasn't changed in nearly 50 years.
A Star Trek series set solely on a post-apocalyptic Earth and focuses mainly on reconstruction would be good for a two-part flashback episode in an existing starship- or starbase-based series, but I doubt that premise could hold an entire series long by itself, IMO.
A Star Trek show gotta have a starship in there somewhere. Even DS9 knew that--first with the little runabouts from episode one, and later with the Defiant