End users need to be involved in the design of facilities, simple as that.
Best baby change I ever saw was in Debenhams Cardiff. Separate to the accessible/disabled toilet, had full sized and child sized toilets, sink, proper unit for changing the baby rather than fold down (DS hated the fold down ones, would scream the place down), loads of space, more than enough for a double buggy. It was brilliant.
Worst, outside of not having any, was a fold down baby change in a rather small cubicle. Couldn't get alongside it so with DS hating the things anyway it was useless for us. Floor was really wet so couldn't change him in the floor either.
Nothing to do with baby changes, but one memorable public toilet had cubicles so narrow that with the toilet roll holder narrowing it further it was difficult for me, size 12 at the time, to turn round in the cubicle. Older facility so originally it wouldn't have had the massive toilet roll holder, but did nobody consider the impact on users of adding them? Larger women, heavily pregnant women, would find it impossible to use, couldn't have taken a toddler in with me, anyone on crutches would have found it extremely awkward or impossible. Just having a large bag would have caused problems.