Help to buy has certainly pushed prices up.
IMO a lot of people are seduced by the ‘everything shiny new’ factor, and, (as they think) no problems/maintenance/decoration for a few years. Too often to find out the hard way that this is not the case, though I know some builders do still have high standards.
When I was looking at flats in a non-central London area with a dd some time ago, there were new build flats of 45/50- ish sq m going for the same price as e.g. many purpose built, 2 bed Edwardian maisonettes of 68-70 sq m, in much nicer roads not far away, no further from the tube station, with on-road parking (none at the new builds) and many with their own tiny garden or outside space. Many had also been very nicely renovated - if not they’d be quite a bit cheaper.
And typically the older properties would have way lower ground rent/service charges. Usually a small fraction of what they’d have to pay at a newbuild.
Yet the new flats were selling, and I doubt whether it was all to landlords. I can only think people were seduced by very cleverly staged, shiny and ‘stylish’ show flats.