I think a great problem with Doctor Who today is that it is of a very specialist genre (science fiction/fantasy) of which British television Producers/Directors/Writers/schedulers aren't really educated about or trained on how to produce. There's an additional problem as well as many in the industry likely do still turn their nose up at the genre and consider it inferior, that or the are afraid of it... as the great Philip Hinchcliffe has pointed out when commenting on his time on the show - "This was the show that could find you out." It would test the mettle and capabilities of the people who worked on it and show their limits, expose their lack of grit and ability to handle anything other than straightforward basic drawing room drama's.
Unlike America the British talent pool for genre television production like this show requires is very small, there are very very few people with either the training, the aptitude, or the will to take on such a unique show and be understanding and capable enough to meet its challenges. And this is why the BBC ended up with little alternative but to target Chris Chibnall. They believed he was the best choice in a drought of candidates as he had already experience with he series and had Producer credits to suggest he might handle it.
I suspect the reality is there is either no one out there who wants the job running the show, or the ones who do raise their hands are the type of candidates who simply don't have the obvious experience and skillsets required. In a real sense this is one factor that shows just how flawed and unworkable the concept on the one-man Showrunner actually is... there are precious few talents who are as willing and capable of driving Doctor Who forward as Russell Davies and Steven Moffat very demonstrably were.
Think that the Star trek Franchise gives to us the blueprint to having a successful Sci Fi show, as they have had multiple shows and series, and pretty much have kept a solid core of writers, crerw, producers, and directors to keep moving forward the ongoing saga of the USS Enterprise!