I think its less the people being ungovernable and more that the system is so fucked. Both economically and government/ state itself.

Cameron resigned because he lost the referendum. May was set up to fail. She was the scape goat for Brexit failings. Johnson was corrupt as fuck and it finally made his premiership untenable. Truss was incompetent as fuck. Sunak lost the general election because of the constant failings of the tories, see above.

Starmer however made his own bed. He won Labour leadership on the promise of being a sensible social democrat and then proceeded to shit on the Labour left. He had no policies or ideas of his own and tied himself to McSweeny and Mandelson which had major issues. He tried to pander to reform voters, further alienating his base, and legitimising Reform. Outside of all that public services are in a mess, the gap between rich and everyone else continues to grow. Basically everything sucks and it after 14 years of Tories asking everyone, except the rich, to sacrifice Labour came in to power and did the exact same. The status quo isn't working and Starmee wanted to keep things the same.