I don't know how much simpler I can explain it, you keep misunderstanding. I'll use your example.
Standalone PSVR2 ($399) Hardware is in the unit so it is pricier than the add-on by itself.
PS5 ($399) + PSVR2 as add-on ($150-$200) Add-on headset is CHEAPER TO PRODUCE since it has NO HARDWARE in it.
To the people that own PS5s already, a cheaper add-on headset is easier to swallow, than purchasing a standalone that has no connection or compatibility to the PS5, is a seperate ecosystem, as well as being underpowered. Yes, the combined price of the PS5 and PSVR2 might be more expensive than the standalone, but the standalone is a worse value proposition since it is a separate ecosystem, will have worse visuals, and the portable battery will be drain doubly as much powering stand-alone hardware and the screen simultaneously.