I think that part of the problem is the trend in the last few years to "man" rest areas 24 hours a day by contracted "cleaning" crews. This was thought to result in decreased vandalism and lower crime.
What actually happened is that those contractors did what should have been expected. Low balled the first contract bid and steadiy rose their prices over time. What this results in is higher and higher costs states feel they cant get rid of.
There are plenty of companies out there making modular bathroom systems (see some Parks)that are virtually vandal proof. They are low maintenance and can be hosed down.
Other states have invested millions in overly fancy grandiose rest areas that are like mini cities. These soak up more millions in upkeep and those contractors. Thus smaller more humble but badly needed rest areas get closed.