In what price categories of hotels have you seen this?
It's actually a trend, but not quite what it seems at first glance. Yeah, there's savings involved - hair dryers go missing, break down, get taken as souvenirs. But that's not really the main thing. Hotels move hair dryers to the front desk also to control who uses them: you can track theft, catch electrical issues, monitor the equipment's condition. Plus it's easier to organize maintenance - you don't have to check every room daily.
I've seen it not just in budget chains. At mid-range and even expensive hotels it happens, just there they hand over the dryer faster and the service is more polite. Although, of course, at luxury places the hair dryers usually stay in the rooms, because they have different clientele and a different service level.
Here's what matters: if a hotel gives you a hair dryer on request but it's bad or broken - that's a minus for comfort, don't confuse it with pure savings. Worth checking when you check in whether it even works, and if there's a problem - report it to the front desk right away instead of dealing with claims later.