The US political system is structured in such a way that it's very difficult to draft legislation and get it passed. You have to get a bill to pass a majority in the house, then (generally) get 60% in the senate, then get past the president's veto, and then implementation of that legislation will fall to a governmental organisation ultimately run by a political appointee who is appointed by the President and confirmed by the Senate. That organisation then needs to fight out any judgements they make in federal court and are ultimately decided by judges who are appointed by current and previous presidents.

Right, so, lots of stakeholders, very difficult to please. Add to that the fact that the house is elected every 2 years (so 50% of the time it's election year), so is the senate (although only 1/3rd of the seats, so it's impossible to swing the senate quickly), and the president every 4 years. And since the incumbent president's party always suffers in mid-term elections, and since the senate can't swing quickly, a single party has only had complete control of government for 14 years out of the last 50 years.

So basically, the President generally gets 2 years after being elected during which they might have the actual power to draft, and pass legislation. Most of which gets spent on 1 single piece of legislation - for Obama is was Healthcare, for Trump is was repealing Healthcare (failed in the Senate) and Tax cuts.