Agreed. You could find someone on Rover for less, but most families don't want someone they haven't used before in their house while they're away to save $30-$40 bucks. It doesn't make sense. Also, what if new person fails to show up? The last family I did this for had two special needs dogs, who had to take medicine and I had to keep them calm for 30 min. after they ate., etc. So it is a lot more effort on part of family to find someone new who has availability to come several times per day and who they're comfortable letting in their house.
Agree with PP who said having someone drive or take metro three times per day for $15/hr doesn't make sense. Why would I give up a whole day for just a few hours of work?
If you really aren't sure, look at what dog walking or pet sitting companies charge for overnight sitting and charge something similar. They charge per walk and per overnight, with additional for things like medications.