National ISPs like Spectrum/Time Warner Cable, AT&T, and Comcast/Xfinity have an oligopoly. They have divided up America into their own markets and purposely avoid entering each other's markets to avoid competing with each other. With no competition, they are free to charge as much as possible, avoid providing good support, and can provide suboptimal service (ie, low and asymmetric download/upload speeds, terrible latency). [1] The problem worsens if you live in suburban or rural areas. Of course there are exceptions where coverage overlaps due to sharing infra, but that is rare and possibly priced in.

[1] https://www.vox.com/the-goods/2020/2/18/21126347/antitrust-monopolies-internet-telecommunications-cheerleading