It cuts across every demographic. Under 25k household income - a good 40-50% of households have a car. Housing estates - tons of cars. Well off - almost everyone.
https://content.tfl.gov.uk/technical-note-12-how-many-cars-a...
It mostly comes down to whether someone has a need (e.g. has children, fairly mobile in their job, has family outside of town, enjoys going on road trips etc) and actually wants to pay for it rather than anything else.
In addition to that, a bunch of stuff happened basically at the same time. We got ULEZ, we got a ton of low traffic neighbourhoods (e.g. streets where cars are not allowed at certain times of day regardless of emissions), we had COVID meaning that habits and demographics changed, we had Brexit which probably had some minor effect, etc. All of that happened within about 5 years and I don't think you can isolate any of them.
I don't really find most discussions about it interesting as a result of all of the above - it usually just ends up with someone trying to find evidence for their pre-existing position rather than anything that feels actually scientific, unfortunately.