Non drivers benefit because workers at the businesses they patronize don't have to pay for parking, delivery people don't have to pay for parking, visitors don't have to pay for parking, etc.
The point I'd make is that mandating minimums of free parking is absurd: businesses and developers could instead decide how much parking they anticipate their business would need. They could come up with many creative solutions somewhere between the extremes of zero parking and plentiful free parking depending on the area. In most towns and cities across America, except for a few dense urban cores, we mandate one extreme and the result is higher prices for everyone (including the non-drivers, who get to help pay for all that unused parking as well).