I would have sympathy for someone who had developed mobility problems some years after getting their dog, but the dog poo on the streets has very little to do with people with disabilities. I've seen a lot of fuckers in the act of just leaving it behind them, and I cannot believe that they all had invisible disabilities that meant they walked easily without any apparent discomfort, but couldn't scoop.
wheel chair user with a severe disability and physically therefore unable to do it
It won't be a wheelchair user. Wheelchair users suffer worse from dog mess. Imagine for a moment being in a hand wheelchair, like this, having just accidentally gone through a pile of it. It goes all over your hands as you turn the wheels. It's a lot harder to avoid if you're in a wheelchair, too.
Have a proper think about that. If you're out on your own, you have to touch those wheels to get back.
And even if you're in a powered wheelchair, and don't have to turn the wheels by hand, it's still worse for you than a ordinary pedestrian, because ordinary walking folk can leave their filthy shoes outside or on the mat. Wheelchair users sometimes need their chairs to go round their own house. So they're going to have to somehow scrub those wheels or find someone who can, or accept spreading dog mess over the floor.