I think misplaced cynicism about election promises is causing a lot of people to work too hard on “why did the Tories lose so badly?” It’s not that deep: most parties keep at least 80 per cent of their pledges. This one…really the only one is that they didn’t raise VAT. How else was it gonna end?
(The cynicism arises IMO because parties more regularly break their implicit promises: the Liberal Democrats implemented most of their manifesto 2010 to 2015, but they had spent a decade implying they were to the left of Labour, so people felt betrayed.)
My gut feeling was the Reform vote was mostly people who would vote for a Tory party that did what it promised. Of course, not great that Reform was the "natural" choice for such a large part of the Tory base.