I’m not sure why parents aren’t more angry that their children aren’t getting the education that they deserve because of how poorly staffed many schools are to be honest
In very general terms, this has always been a thing - or at least it has since I started teaching (2002 
When I started, recruitment was primarily different in maths (nothing has changed there!) English, MFL, science and ICT. Various incentives were offered to make the PGCE attractive. Yet the TES forums were filled with experienced teachers unable to get full time permanent work, there was a lot of concern about TAs covering classes as this was detrimental to many who were relying on day to day supply.
Over the course of the 00s, while some subjects had an overall shortage some areas and some subjects were doing just fine for recruitment and there was a surplus of teachers, while in some more expensive areas it was always harder to recruit.
Teach First started life as trying to get people who would perhaps ordinarily have gone into a more lucrative career to give teaching a go: it’s now ah, not. There has been talk (while I’ve been teaching) of ex army officers, retired postal workers, various schemes and so on.
Stats tell one story, but someone’s school may tell an entirely different one. And many of the schools who struggle most to recruit and have the most turbulence in staffing will often have parents unlikely to complain.
I also think that a lot of the stock phrases have been overused and thus have lost their impact.