I do understand why its a shared facility in some places, old buildings where adding another cubicle just isn't possible.
But many places - supermarkets, shopping malls, massive stores like Ikea... there is no fucking excuse.
They could add an extra wide stall into the mens and the ladies, they could provide a family bathroom (some Ikeas do, not all though, the newer ones do). They do not bother, because there is no comeback for not bothering.
Disabled people have no effective way of complaining.
Parents happily use the facilities and they are the bigger voice here and could complain but they don't because its only an issue for them (and not much of one) for a couple of years per child.
I've had to go to the loo with the fucking door open to the public, because the accessible toilet wasn't and i couldn't get close enough in my chair, get on the loo and shut the door - not just the once either, multiple times in various places (all relatively new and large buildings too).
On several of those occasions, the only reason I could not get my chair in was due to the fixings for baby change stations/nappy bins!
Yes, I complained, but supplying the needs of parents is bigger business than meeting the legal requirements of disabled people, and as I say, there are no real penalties for offering substandard facilities.