There has been a real problem with recruitment of suitably qualified teachers in maths, science, languages, and a number of other subjects, for years. That is because teaching is really bloody hard, often unrewarding and Gove's measures are merely heaping shit on everyone. Teaching is not indentured labour and there are easier and far pleasanter ways of making a living than having chairs thrown at you by hostile and disturbed teenagers. Contrary to popular opinion, it's not a job people have to do because they have no choice- people are making that choice. As long as conditions carry on getting worse, people will carry on leaving and SMT will carry on struggling to recruit suitably qualified people. And still even on MN you'll get people bleating that if teaching is that bad, then why do people stay? The answer is they stay for as long as it takes for them to realise they really can't change it all single-handed, and then they leave.
It does not surprise me tbh.