There are two difficulties with people like David Walliams.
The first is that they produce an amazing and / or popular body of work - not always the same thing, , and TV producers and commissioning editors think that they will always produce that level of output forever more.
The second is that because someone has been a huge success in one specific and rigid format, that they can be equally good and successful in any other format.
Both these premises are utterly false - which is why David Walliams, a clever sketch writer and credible actor, is totally useless as a chat show host saying lines written for him by other people, and trying to hold meaningful conversations on TV, which is actually far harder than the professionals make it look.
If you analyse most of the failing formats, it is for exactly that reason - someone has seen someone do one thing, and assumes they can do another equally well, and it never works out.
John Bishop may be quick-witted enough to think on his feet in conversation, but again, he will have fed lines to read out, and conversation which he may fail with if his guests are not suitable, or he doesn't gel with them instantly.
As for people like Gordon Ramsey - whose bright idea was that????
We shall see ...