I agree with the drop in new builds, and in particular the right kind of new builds. There are other supply side issues that I mentioned, like second homes, airbnbs, investment properties etc. to add to that.
I also agree that population increase is one of the main issues - although as I've pointed out many times now, population increases over the last 40 years have been as much about demographic changes as net migration.
And if household sizes are coming down, then that's a huge factor too. If the population had stayed the same size since 1970, we'd still have needed around 25% more houses, just to meet that change in how people want to live.