I'm in Scotland (Glasgow) but can't answer your question about why there so many vacancies. But I did find this on a Google search - and some of the related links look interesting too (eg the high number of teachers due to retire).
It looks like there is a commitment from the Scottish Eexecutive to raise the number of teachers - despite the falling birth rate.
What do you teach and whereabouts were you thinking of? The rules in Scotland are (or were when I was at Uni - albeit a long time ago!) stricter in Scoltand than in England about what you are allowed to teach, ie you can only teach what you studied at Uni AND what you then did your teacher training in.
I also seem to remember my Mum (a former English teacher) complaining that teachers ion Scoltand had to work about two weeks longer per year than the teachers in England. Not sure if that really was the case - or even if it still applies.
Teachers up here have some kind of agreement on working hours that was certainly better than England a few years ago, not sure if that's still true. If it is, I guess that would create more vacancies as all teachers have to have a certain amount of out-of-class time each week, so there are lots of "promoted staff" that mainly do admin and filling in for class teachers when they're out of the classroom. I don't think the holidays are any worse now, although the summer is much earlier (back mid-August).
We are in the middle of relocating back to Scotland I had applied to do a PGCE in Primary but pulled out of the interview for a variety of reasons, primary is very difficult to get into unlike secondary for some reason.