Pro's better in every department. Noise Cancellation is the baseline now, & if you have an iPhone, the AirPods Pro are pretty much essential, but if they don't fit, then the OG's may be the way to go.
I just received mind in my AirPods Pro in the mail a couple hours ago. I used my AirPods 2 as a bluetooth, kept one in an swapped them out throughout he day. For me they would disappear in my ear, never fall out and just be comfortable.
Although I haven't given the APP an honest chance they are already bothering my ear a little. The AP2 weren't a tight seal either and since all I was doing was talking on the phone it was nice because I could hear around it. The APP feel like my fingers in my ear and spatial awareness has a slight hiss.
I know that is a specific case but you wanted a reason so there it is...
I've used both extensively (so much so that I've owned multiple pairs of each) and although the Pro's do have better sound quality and the noise cancellation, I prefer the regular AirPods in probably 80%+ of cases for these reasons:
the case is smaller and more pocket-friendly
they fit in my ears more comfortably and don't fall out as easily (not that the Pro's fall out that easily...)
they're much more comfortable to fall asleep in at night
they have tap-to-pause functionality vs. Pro's needing a button to be pressed
seemingly better battery life, though I haven't tested this or researched