It's not necessarily about physical disabilities. Think about 1 parent with 2 young children and 3 bags of groceries. And that roughly fits a LOT of folks. Maybe if both your house and the grocery store (or other destination) are within 1-2km of a mass-transit stop you can use that - otherwise it's pretty much personal car/bus. And if that's the case for one particular trip, you still need to have this option for the others.
It's a norm to see mothers riding two children on a bike here in Tokyo. Grocery stores are typically in walking distance, so no need for the bike ride for that.
Note that reliance on cars leads to grocery stores not being within walking/biking distance, and less cars (and denser cities) leads to more livable cities.
The goal is to make it possible to bike places safely, which makes it easier to transition from reliance on cars to better forms of transportation. No one is suggesting that we switch everything over to bikes right now.
