Partly because running a major campaign in the US requires a lot of money, so candidates are compelled to fundraise large sums. This means lobbyists have a built in method for getting the attention of candidates and candidates have a reason to listen to them.
European elections, in general, don’t require the vast sums of money so lobbyists have less pull.
are smaller. The population of the United States is approximately 40% of the entire population of Europe. Gavin Newsom represents more people than the entire country of Poland, and Poland is the 8th most populous country in Europe.
And, as I understand it, the election (and more specifically, the campaign) cycles in the U.S. are far longer, at least for Congress, the presidency, and state governors, than in most parliamentary governments.
U.S. Representatives face re-election every two years; they are, in essence, always in campaign mode, to a greater or lesser degree. Similarly, candidates for the presidency are often forming exploratory committees, traveling to early primary states, etc., two years or more before the general election (and a year or more before any primaries actually begin).
By contrast, as I understand it, in the UK, while the next general election must be held no later than January 28th, 2025, it could happen before then, as Parliament could call for a a dissolution, and a new election, at any time. And, once an election is called for, it happens five weeks (25 working days) after that point.