I've always assumed that the reason there aren't many launch sites in Europe because the booster stage falls back to Earth, and generally you want that to be over the sea. People get cross if rockets fall on their houses. If you're using the Earth's axial rotation as a helper that means launching heading east, and in Europe east is pretty much always over land. That's why most spaceports are either by an ocean (USA, Japan) or over a huge area of land no one lives in (Russia).