As with many things, there are probably several answers.
1. It would seem that whoever is in charge of each park (Park President or VP?) just isn't very interested in routine upkeep and maintenance. I worked for a company once and the owner used to walk the property daily looking for the smallest of details in order to keep everything clean, orderly, and working properly. He took pride in how things looked and worked. Does park management do this? Over-flowing trash cans and scattered trash and clean restrooms to me, is a bare minimum of expectations.
2. Regarding attraction maintenance, see #1. The Park President should fight for necessary maintenance budgets. Park cleanliness and ride up-time (or downtime) should also be a part of the Park President's evaluation ...... if management cared enough that is.
3. I have no idea of this, but it would appear on the surface that profitability and stock price are the only bonus drivers for Management at all levels. Operational metrics (such as cleanliness) are not apparently valued as much as they may have been 30 years ago.
4. The public in general is less and less interested in doing their part. It is incomprehensible to me to see someone throw trash on the ground. But it happens more and more every day. In much the same way that we don't take as much personal pride in our appearances anymore (business casual keeps getting more and more casual), society at large seems to be less interested in respecting their surroundings and other's property. It's just a dumbing down all around us.
Bottom line, as I've said many times (and others as well), if the parks continue to be packed and profitable, Disney Management will continue spending less and less to keep them looking and working great as that maintenance budget ends up in Management bonuses. Is society so far gone that Management and Leadership everywhere is more concerned with personal compensation than they are in having pride in your product, especially if it costs a little more?