In a word, Thatcher. A gross oversimplification, obviously, but that era effectively destroyed natural (e.g. monolithic industrial workplaces) and constructed (e.g. unions) sources of solidarity, ushered in fragmented individualism across our daily lives and knocked the very idea of class, both Marxist and socio-economic, out of the public discourse. I've never known any different, personally.
None of the above is an absolute and nor is it a linear path to total destruction but it's hardly the picture of good health.
So I wouldn't say that PP has become stronger as such, but that the alternatives have gone so it becomes the only recourse. There's yet to be a recovery and reforming of old, large-scale ideas of solidarity to fit the modern landscape. So we see a gov.uk petition or a food bank collection at Tesco instead of organising or a general strike.
This is happens beneath the relationship between government/state and capital, so absolutely capital is the fundamental driver of change, but the discussion has been about how that's handled, mitigated, suppressed or whatever.