there are a lot of reasons that american presidential elections take so long but a big one imo is just money. it takes time to raise a billion dollars.
others include our ridiculous and arcane system, how big our country is compared to european democracies, etc.
It's one of those things where I honestly think almost every American would love 2 month elections, but will absolutely never ever be fixed because of how much of a cash cow of an industry elections are.
Most don’t appreciate the sheer logistical task of holding a US election, which is largely delegated to counties or municipalities with minimal staffs who may or may not have add’l non-electoral duties. Doesn’t have to be that way, but it is, and it takes time to do it without major mistakes.
Another big factor is that the Republicans have a 24/7 propaganda network that is entirely focused on slandering the side. This has to be considered in any media spending calculation.
I think it is the precise opposite. They cost so much money BECAUSE they take so long, and money matters more. Media makes more money, too. If the election season were shortened by law, it would become cheaper.