Europe is very hostile to gene technology in plant breeding. A lot of the technologies developed after the 1970s are banned in plant breeding (while they are allowed in medical industries). European legislation also regards CRISPR editing as GMO, and most GMOs are effectively banned in Europe. In America, GMOs are typically allowed, and in America CRISPS editing is not regarded as GMO.

If you are a plant breeding scientist, you can either work in Europe with your hands tied behind your back, or move somewhere else and innovate more freely.

I am sure there are other equally important reasons, but this is one.