Something that I think a lot of people don't quite understand is how physically big London it. There are entire areas that I've never been to, despite living in this city my entire life.
For comparison let's take New York, which has 8.47 million people (according to the first result on google), compared to London's 8.92 million. Pretty comparable sizes and they're both known for being large, diverse, central cities to the respective countries.
New York has a land area (again, according to google) of 304 square miles of land (and about 100 of water but this is just looking at the land). London has a land area of 607 square miles.
That's almost twice the area for roughly the same population.
So yeah. When I say "oh yeah I've never been to *insert area here* because it would take too long" I'm talking 2-3hrs, 2 buses, and 2-4 tubes or trains. Not 30/45mins to an hour. 30/45mins is how long it takes to get to my nearest shopping centre. And that doesn't mean I don't live in London. London is just weirdly physically big.
(Yes part of the reason is western European vs American city structure, but other western European cities have several million less people so dont have the issue to the same extent. The western European city with the next largest population is Berlin at 3.85 million and a similar land area to New York. There are larger cities in Europe than London but theyre in Turkey and Russia and I know nothing about how cities are structured in those countries)