You're mistaken about how easy it is to find remote developer work. Upon moving to bf Lake District, I had no trouble picking up a gig for an American company at my Bay Area rate.
There are enough companies hiring remote workers these days that I can't understand why anybody in England continues to put up with comically low and out of touch with reality London rates.
Are you seriously trying to generalise from your experience as one person to an entire city?
There's certainly enough remote work going for you to find a job. Or for everyone reading this page to do so. But there are over 100 000 people working in IT in London. Are there 100 000 remote jobs available?
Remember, we're not trying to find remote jobs for everybody in London. Only enough for the ones smart enough to move someplace nicer and take a job with an American company.
Also keep in mind that every developer job is a remote one. It may not be advertised that way, but if you've proven that you're good at what you do and you decide to move out of your felt cube and claim back your quality of life, your company will find a way to accommodate that (if they're smart enough to do the simple arithmetic to calculate what it would cost to replace you in this market).
There is going to be a tipping point if London property prices continue to rise. There's no point in having a start up in, say, Shoreditch if you can't afford to pay living salaries to people to work there, so either you a) move somewhere the salaries and office space is cheaper or b) you go remote and increase your talent pool. There's quite a few startups that have to be in London (e.g. they work in the finance industry) but there's likely more than a few that really don't need to be.
There are enough companies hiring remote workers these days that I can't understand why anybody in England continues to put up with comically low and out of touch with reality London rates.