I have several thoughts on this.
Cars massively degrade the public realm, and make it harder for everyone to get around on short journeys. They require dedicated physical infrastructure, both in terms of things like car parks and big roads, but also in terms of things like grade separations, drop kerbs, confined crossing points for pedestrians etc. All of these things have a massive impact on the built environment, and how accessible it is. Cars also damage their own infrastructure pretty much constantly, which requires huge resources to repair. Removing the bulk of cars would allow a complete re-imagining of how we use our space, and free up money to better maintain it. This would benefit everyone, but would also make it far easier for a lot of people with mobility disabilities to move around on short journeys.
I also think this is an argument used in bad faith by a lot of people to maintain the status quo, which I think is ultimately very damaging for disabled people in a lot of ways. Our broad societal reliance on cars means that homes are often located far from services - particularly cheaper homes, and as disabled people are statistically more likely to be on lower incomes, that I’m fairly sure impacts on them more. Again, moving away from cars as a dominant form of transport would allow us to re-assess how we do these things.
I guess also fundamentally nobody says “ban all cars” in a vacuum of thought. I favour a massive expansion in public transport - primarily light rail, which is fast, comfortable and accessible these days, but also buses. I’ve said this before on here, but its literally only a lack of imagination that holds us back in this. We apparently find it easier to dig giant tunnels under London than we do to build trains that run on existing streets. It speaks of a paucity of ambition more than anything. We can do better.