The OEM sensors may be tied into the 360 degree camera system, so if that also isn't present, those sensors may not be able to be added. There are of course aftermarket sensors but not sure how integrated those could end up being and then it would just be an audible alert, I'd assume.
One reason I went for the PPT trim because I was used to the 360 & sensors from my 2019 CX-5 Sig. It really helps with parking in my garage due to limited space, and pulling in and out of public parking areas (particularly parallel parking, which I suck at). What's nice is that the camera and system in the CX-50 is significantly improved from my CX-5's--clearer and wider camera views, and the guidelines adjust with the car's movement. So, the added expense overall was worth it for me, but others may not feel the same way.