I suspect there are three main reasons why younger teachers are contemplating emigrating. One is the quite poor pay scale for a graduate here in UK. One could earn more in a trade or small business.
I imagine graduate teachers abroad do far better with remuneration.
Secondly, the appalling behaviour and manners of youngsters who are unable to concentrate for more than five minutes must drive their teachers crazy. I would be itching to lob a large text book at their blasted heads. I've watched programmes on TV where the secondary pupils are all of a twitch like the inmates of some sinister mental hospital, shouting, posturing, swearing, fighting, running about the room. No-one can teach anything at all under those conditions. I've seen classes abroad (in Spain, France, Ghana, Senegal and Ivory Coast) where the pupils sat calmly, all eyes on the teacher, respectfully responding to questions or writing neatly without talking to eachother. Bliss.
Thirdly of course, it's the utterly ridiculous amount of monitoring of every move the teacher makes, or even proposes to make. Every minute of the timetable is prescribed by the Mr Gradgrinds of the DoE. I remember after 30 odd years in the profession having to write very detailed lesson plans for each week, then reports of how the week actually went. This included equipment (a pencil, a book...?) It was like teaching by numbers, and killed any vocational creativity. And it took hours and hours of my time.
During our Ofsted inspection, one of their team actually stood in the playground every break and lunchtime, "to observe how the duty staff interacted with the pupils." Clutching a rapidly cooling cup of coffee and dying for a wee, were we supposed to bloody play with the children as well? Absolutely totally ridiculous.