Why is "random perks" bad? Isn't the best interest of the company being making the employees happy so they are more productive?
The negativity around giving "random perks" makes it feel like you're running a prison, where the point is to punish people instead of a workplace.
It might just a CYA move on the part of an individual actor in middle management. The manager doesn't want to risk getting penalized for handing out "random perks", but also doesn't want to get in trouble for ignoring a "medically necessary" request.
Put another way: That seemingly arbitrary behavior might make more sense if you assume that it's intended to protect an individual, rather than to protect the corporation.