The coalition of Labour voters was not homogenous. It comprised progressives, liberals and small c conservatives who disliked the tories for historical and eventually generational reasons.
A lot of the latter were what we are now calling Red Wall tories. Anti immigration, anti internationalist, pro workers rights but limited to a form of nativism. It’s this group that has peeled off recently, and a lot of that is due to Brexit.
There were of course poor and/or working class people who voted Tory before that, otherwise Thatcher would never have won, but the big shift has been since 2016.
The tories are now gambling in losing them though, and feel their new leadership doesn’t speak to that cadre like Johnson did (how you can think that Johnson relates to you if poor is a question for another day, but people did). This mini budget is about getting back the wealthier people the tories lost to Brexit, many of whom vote Lib Dem now and were the cause of the Lib Dems’ massive by-election win in Chesham.
Which brings me to the other point - a lot of people here seem to be assuming a) poor people should be socialists and b) socialism is inherently progressive. In both cases - not necessarily, be careful about those assumptions.