The barriers to mobility are the giant, dangerous roads and parking lots between everything that car dependency requires. Cycleable/walkable places with good public transit are easier to get around for everyone with or without a car, regardless of disabilities.

Also, disabilities exclude more people from being able to drive than from walking/cycleing/using public transit. Not to mention people excluded from driving due to age. Or finances. Or not being able to get a license due to lack of English literacy. Or not having a permanent address. Or people that just would prefer to not drive. All these people deserve the right to be able to get around, and car dependency denies them that right.