Arguing whether people cycle or not is monofactoral is a cycle-path to nowhere, of course it's a combination of things, both practical and cultural. I'm not sure anyone really thinks that [high quality] cycling infrastructure is the sole arbiter of whether a person gets on a bike or not. But being able to get from (a) to (b) is a way that feels and is safe is a key part of people's thinking. The prospect of bouncing down the gutter of an A road to an accompaniment of speeding, close-passing traffic isn't one that is ever encouraging cycling (indeed my first 'commutes' into central London were excused by the proximity of the Waterlink Way, which while not exactly ideal infrastructure, offered a mostly traffic-free route as far as Deptford). These days, when I regale people of my ride home down the A23, the typical response is similar to if I'd told them my new hobby was learning to juggle unexploded ordnance.
I would argue that without a clear way of safely getting from (a) to (b) without having to undertake vehicular combat, the hurdle will be such that most people won't contemplate cycling as an option. Having lived in Croydon and Bromley in recent years (and now just beyond the London pale in Surrey) where there is no cycling infrastructure, well, effectively no one cycles (other than the occasional person who has mistaken the A22 as a good way to get the North Downs and beyond and the few inveterate malcontents like me).
Yes, there is culture. London is relatively unique when it comes to cycling (and yes, I'm one of those affluent middle-class types who feels secure enough not to turn up everywhere in a Mercedes). But in addition to types like me, there's a combination of youth, perhaps a more a gung-ho attitude to life, expensive travel options, and a need to commute.
Anecdotally, 12 years since I hopped on a bike one Sunday to cycle up the Waterlink Way, all the way to the leafy Regent's Park surrounds of the Royal College of GPs (which seemed an epic journey, and yes it rained), there are certainly a lot more people cycling in London. I work by one of the new cycle routes (Blackfriars Road) and it's packed during peak times, and every morning I'm part of a peloton from London Bridge along Southwark Road. Despite it being a shit route, CS7 (which I sometimes get), is probably oversubscribed by the number of cyclists (leastways till South Clapham). In that respect, it's reassuring.
Demographically, it's not changed that much. It's whiter than a KKK rally, and there are probably more women, but you're unlikely to run out of fingers counting them (don't do this, they'll think you're odd). The majority are still 'roadies' (and that's not a judgement, just an observation). As a bloke who ambles along in his chinos (I am that stylish), I'm still a bit casual for the movement. I expect if you plotted age-adjusted income quartiles, we'd all mostly be in upper quartile. I speculate that's in part that we don't have anything to prove (or we're proving it by not proving it). The social status psychology of car usage and ownership is one of the more difficult things to unthread, there have been decades of effort and advertising entwining social status and personality with the car (which, I find sad, but if you're a young black man on a council estate in south London, I can at least comprehend why you don't wake up every morning and wish you had a road bike).
I confess, I've seen little conflict with pedestrians (and I'm both). Yeah, there's the occasional dick, but outside of the newspapers most people get on reasonably despite their mode of transport.