Each port can accept or give power (at various voltages) potentially or act as data sink/source (determined on connection), or have alt modes.
Such device would be either quite "fun" to use, unless it had type C ports marked with dedicated functionality, so you'd have to be careful what device you plug to what port.
AFAIK there's no protocol to control other ports via PD from the port you'd connect to the "main" device (like your laptop). So the behavior would be all pretty random, or the ports would have to be fixed in function.
My completely unfounded on anything guess is that it might have to do with breaking the chain of "trust" between the different connectors on negotiating how much power an actual downstream device can handle.
I don't know about the power rating thing so much. USB-PD is a lot more complicated than having a dumb brick with a rectifier and regulator. And while I trust my cohort of wall warts not to burn my house down, I spend way more on 3rd party USB C bricks because I have no faith in anything I buy on Amazon.
- Apple made some different standard that uses the same Plug
- Power supplies come at different power ratings (who would have thought!)
Of course this is not ideal, but it is already better than not being able to get _any_ 3rd part power supply at all.