Sorry for the delay, missed your question until now.
We opened the office in Poland originally because there was a group of programmers there who were experienced in a complex and somewhat esoteric programming area that my company was working in (digital electronics simulation).
But it's worked out well, as there are some talented programmers there, and the labor cost is much lower than the US and many parts of Europe, so we've continued to expand there with time.
Thank you for your answer