It’s really down to the simple fact that most people aren’t aware. And those that are feel powerless to do anything about it; “It’s been this way for so long, it’s part of how life is now.” (see also: the NSA spying complex) Not to mention that ISP monopolies aren’t near the top of people’s “policy priority list”(TM) (contrast with, say, abortion), so even if a politician were to campaign to fix the problem, most people wouldn’t care. And because of that, most candidates don’t campaign that much about ISPs because it’s (essentially) a waste of ad money.
Take Ron Wyden (D-OR) for example. He’s been talking about the problems of “Big Tech,”[a] the NSA, etc. for years, but no one outside tech or his state have even heard of him.
[a]: Those aren’t “scare quotes.” They’re because there isn’t really a good word for it. FAANG seems too restrictive compared to how many companies are actually part of the problem.