The sheer incompetence. It's pretty clear that, past the second term, they're pretty much scraping the bottom of the barrel, which was originally full of people who weren't really qualified to run any of the departments they were responsible for in the first place.
I mean...austerity was a reasonable response to the crap that the previous government had left us with. If Cameron's government weren't idiots in the second term, it would've put us in good stead for moving forwards...but they weren't, so it continued. And then, because it wasn't really working, we got Brexit, which set the stage for the real incompetents to come forward, and...well, add a global disaster to an already wrecked country that was supposed to be entering recovery but managed to assiduously avoid it, and here we are.
Labour can't fix this - nobody can, in even two terms. We might be able to recover a bit, but it's going to be more than a decade before we're even approaching parity with where we were even five years ago, much less the heydays of the early 2000s.
Not only do we need to get the current shower of shit as far away from government as is possible, we need a series of boring, more-or-less centrist governments to just knuckle down and get the job done.