Comparing the cost of single-day tickets between July 1983 and August 2018 is interesting. A single-day, single-park ticket for August 2018 is $116.50 (averaging the different prices for MK and the other parks). In 1983, the first full year of EPCOT Center, the cost was $16.00 (average, taking into account a price hike in Oct 1983). Adjusted for inflation, $116.50 in 2018 has the buying power of $46.18 in 1983 dollars.
Combined attendance at the MK and EPCOT Center in 1983 (the first full year EPCOT Center was open) was 22.7 million. That means that Disney was pulling in $363,200,000 on admissions alone. The parks were spotless and attractions were kept in top condition.
If the cost of admission in 1983 had been equivalent to what we pay today, they would have made $1,048,286,000 on admissions.
In 2017, the four WDW parks saw attendance of around 56 million. If we assume that this year's attendance will be similar, for the sake of argument, they would conceivably bring in $6,524,000,000 from admissions.
The long and short of it is that they could absolutely afford to keep the parks in top condition. They simply choose not to. Guests should expect more from what they're paying for a WDW vacation. Having the money is not an issue. They have money. Until guests start caring and making a fuss and, to be honest, take their dollars elsewhere, there is nothing to convince me that the trend of neglect will stop.
I'm far from a mathematician or statistician and I realize that my numbers are approximations, at best. However, I think that it at least gives a high-level overview of the disparity of the value the average guest received from their ticket price in 1983 compared to today.