When I first went to WDW as a kid I was 6 years old. It was for the bicentenial celebration (1976) and I can remember all of the adults in my party were smokers. Both parents, two aunts, two uncles, and my grandmother. Back then lots of adults smoked everywhere, all the time. I don't think they smoked on the rides, but they smoked in lines, walking around the park, sitting at tables, whenever and wherever they wanted to because it was the 70s. The thing that impressed my little 6 year old brain the most was that there was not one cigarette butt on the ground anywhere!! I grew up in Myrtle Beach SC, and I can remember how the sidewalks and beach would be littered with them so I guess the absence of them really stood out in my mind.
I guess what I'm trying to say is that people aren't any messier than they used to be, people are still people. The reason the bathrooms at any facility (not just WDW) are a mess falls back to staffing. It's either lack of personell or lack of training. Both are the responsibility of management.
