> They have had good public education for the past decade or two and rank high in international student rankings.

I suspect good public education is a symptom, not the cause.

The cause likely is valuing a good education. Culture always wins. You can give people who don't value it a good education and they'll barely benefit.

Polish education has a long tradition of excellence. Indeed, the last decade has seen reforms that have been heavily criticized for working against that.

I suspect Ukraine and Belarus brain drain to be a measurable factor here too.