I think that's the main issue, they cling to Blairism without realising that Blairism was still progressive-lite, and designed to appeal to traditional Labour voters as well. There's also the obvious that each leader since... is not Blair. It's what Corbyn actually did right, ignoring them.
I mean, Milliband and Burnham have personalities when they're not being coached in government, or government in waiting, Brown looked ridiculous trying to be touchy feely, and apparently Starmer IRL is quick, witty, good company... and at least vaguely progressive.
But as soon as they come within a sniff of the leadership or a senior government post, they go all anodine and Stepford Labour Leader!
(Add Ed Balls to another who once out of government actually comes across as reasonably engaging!)