Much as I want someone to replace Starmer, this decision is not a big surprise, really. Aside from Starmer’s desire for self-preservation, Burnham becoming an MP would have forced a mayoral by-election in Manchester which Labour might well have lost (on current polling, Reform had a slight edge). Burnham had a chance to run as an MP in 2024 without causing that problem and decided not to, so it’s hard to feel too sorry for him.
They could call it ‘the Burnham rule’, for short.
Joking aside, you are right, of course. It’s actually a big deal for (e.g.) the Mayor of Greater Manchester to quit, so it makes perfect sense to have a committee that can say ‘Hang on, is this actually a good idea?’
Additionally, as anyone who recalls the leaderships of Iain Duncan Smith and Liz Truss could tell you, party member driven democracy has its downsides.