Android is built on linux yet it is increasingly locked down and many phones are extremely difficult to get root access on.
So Valve could have followed the phone ecosystem path and pushed as much of the feature set as proprietary code as possible (binary blob drivers, proton proprietary instead of bsd), replaced pacman with a valve controlled package manager & repos, setup selinux to give users no power to do anything and made the deck only able to secure boot steamOS signed by Valve. Technical users may be able to jail break such a device but the majority would not be inclined to.
Valve’s wisdom here is in realizing that the majority are going to buy their games anyway but if you don’t lock the device down then most of the technical users will also buy most of their games whereas if you have to go out of your way to jail break a device to install something fun then that device basically becomes a piracy only device from that point on.
I think the idealization of this kind of spartan living space is basically the same as the cryptobro idealization of unregulated currency.
Over time exposure to reality will result in making compromise after compromise to solve each problem that arises until you have reinvented from first principles the very same standards that everyone else in society already arrived at.