First of all there isn’t one “European model”, every country in Europe has its own system.

To answer the substantive point, it’s extremely difficult to pass substantial laws in the US due to the structure of its political system. The mandatory coalition of the president + 60% of the senate + 50% of the House of Representatives is a much higher bar than any other democracy. So laws aren’t written to be optimal policy, they are written to satisfy this extremely high coalition requirement — Obamacare in particular was very fundamentally weakened from some of the more expansive initial proposals to address the concerns of one or two senators and get them on board.