The majority of who I know that ride share, ride share intra-city. The odds of being picked up while driving drunk in the city are much lower than someone who commuted 20 miles into the city, gets drunk, then has to drive 20 miles back home.
In addition you still have the issue of getting back down to your vehicle the next day. So you're ride share back? That means you're paying double. I think with the impairment of already being drunk they just decide to chance it probably deal with that back and forth headache?