London definitely has fallen. How far is up to you. But it's a horrible place to live in now. Has been for quite some time and it's slowly getting worse.

It's a stereotype based on real world events. It's not deliberate manipulation. People are just tired of shitholes being put on pedestals.

Lots of places in the world are becoming absolute shitholes. There's an underlying condition that's not totally apparent yet but it exists and people can feel, see it and smell it.

Edit: Now it may seem like London is great to someone who has never lived in a place with an actually decent quality of life, which I'm unsure if you have. Places like East Asia, AU/NZ, various other parts of Europe.