I do think one reason children were toilet trained earlier in the past, was the fact of having to wash and dry nappies, particularly in the days before automatic washing machines were common. People had much more of an incentive to get them trained.
I will admit to being somewhat shocked by a friend of dd whose child at 3 1/2 (certainly no special needs) was still in nappies. She was home with him all day, too - presumably it was just too easy to carry on with disposables.
I do sometimes wonder how my mother coped with my two rather younger siblings very close in age, and only one of those old machines you had to drag out, fill by hand, and then put everything through the wringer - though I know even that was more than many had,
Especially in a cold house in winter - no central heating of course - I well remember the old clothes horse in front of the fire, draped with steaming nappies.
Static caravan purchase is it worth buying