Because it's not the same class of device. The PS Portal is very niche. It's a $200 device that basically just runs the PS Remote Play app.

I've used PS Remote Play on my phone and laptop, and it's just not good in the cases I actually want to use it: when traveling away from home. Even with a good Internet connection it's only "okay". It's utterly useless when in transit (trains, places, etc.), and 99% useless in any public place (e.g. cafe or library WiFi).

These are all cases where the Switch, Deck, and similar devices excel. The PS Portal addresses a much smaller market.