It's a modem+router+switch+AP that technically does everything you need, but does all of it badly - really just getting in my way. E.g. it obviously has a builtin DHCP server, but it won't let me set custom DNS. I want to use custom DNS, to block at least some of the ads/tracking on all of the devices on my network; so I have to disable that DHCP and use my own. But the modem resets that setting back to enabled every reboot! (Took me a while first time around to notice there's two DHCP servers on the network, argh). So I've disabled the internal AP, brought my own, and I'm connecting the rest of the network through a managed switch that blocks DHCP to the router.
So I've got one device that tries to do the job of four... but instead I need three devices to do the job of one. I try not to think about it.
Yeah I just have hardware I like running openwrt behind the modem doing all three jobs, with Tailscale Funnel doing the job of port forwarding so I basically never need to interact with the provided modem's interface. Because you're right, it sucks.
The problem is the builtin cable modem. I don't have the parameters/credentials, I have next to zero experience wrangling DOCSIS, and frankly I just don't want to bother. Switching to fiber soon enough anyway.
So I've got one device that tries to do the job of four... but instead I need three devices to do the job of one. I try not to think about it.