And most people don't want to dock their computing device to their TV as a monitor; there are uses for TV-as-output device, and they're well-covered by things like Google Cast and similar technologies.
> You can take peripherals you already own and make a 1-plug docking station without significant cost.
Only if I already own peripherals; i.e., if I already have a desktop or a laptop that I use with external peripherals instead of just the built-in interface. And, I only need a "docking station" if those peripherals are wired, rather than, say, Bluetooth.
Which might be the case for the monitor, sure, but you can already do that. HDMI dongles or cables -- the only one-plug docking station you need in a world with Bluetooth mice and keyboards -- are readily available and not expensive for existing, non-Windows mobile devices.
From a software perspective, Android has supported this forever. From a hardware perspective, there've been Android devices where accompanying docking solutions was heavily marketed, though none in the last few years, because its something users keep not really wanting in practice, even if they conceptually like the idea in the abstract.
Plus, a substantial fraction of the price and size of a "second computing device" that's larger than your phone is going to be the display, so docking doesn't really solve much of anything (especially when the devices are all cloud connected.) There's zero friction moving between by Android phone and my 12" tablet -- with BT keyboard and, if I felt like using one, BT mouse. And I could use the BT keyboard and mouse with the phone itself, if I wanted to. Either device could connect to an external monitor via HDMI with an inexpensive adaptor (and either can cast its display via Google Cast.)
What, in practical terms, does docking solve?