> a few of them were for companies hiring in my exact stack, while also saying they sponsor visas
So you are looking for a job at a very large company which will be ok with you commuting from Bristol to London and that will also sponsor you to move to America?? Thats an extremely specific company-search, I don't think its fair to say that that is any way representative of what its like for senior developers to find jobs.
Also google maps shows that the train from Bristol to London takes 1 hour 40min, so assuming it takes 30mins to the station on both sides, thats about 5 hours a day spent commuting, and I haven't even looked at the cost either. Even if you get 1-2 days a week working from home thats going to be a lot of travelling, as an employer I would be worried that after 6 months or so you will quit because of long commute times.