Late, but it's because most of the time they were. Take this infamous investigation that was done in the 1970s on an institution called Willowbrook that was supposed to be one of the best in the country.
https://youtube.com/watch?v=qzNFRn5TTtcYou have children sitting the dark, screaming, naked, filthy, smeared with their own feces, and infected with parasites, and diseases like hepatitis.
Hell, that last part was even eventually done to them intentionally there as some kind of fucked up study.
All I'm saying is that people need to fucking realize it wasn't bleeding-hearted liberals that got the asylums shut down. It's because they were fucking hellholes that deserved to be shut down.