That might not be a full-time goal. Some want a machine that works on the move but can be expanded to bigger screens and such when at certain locations (office and/or home). A laptop and dock allow this compromise.
It is a compromise, not one suitable for all. But it is the list inconvenient option for many.
I wouldn't say "some". Probably 90% of developers I know require exactly this, in fact off the top of my head I can't think of any who don't. Even the permanent, full-remote, no-really-there-is-literally-no-office types want to sit in a different room sometimes or work from a coffee shop.
It's pretty rare to have a "workstation" setup that cannot be moved.
'... where we came in. Having to buy an external dock is such a compromise! I want to have all the ports on my laptop!'
'But if all your peripherals are connected directly, you need to connect and disconnect them every time, so you have to compromise on mobility. Isn't this...'
And different variations on this same spiral.