HD, I think they are still mandated by the regulatory authority.
Because not many are accustomed to using them or looking for the light, they don't get used much.
The younger controllers tend to not even think of using them. Fair enough, too, I guess. No-one ever seems to see the light, unless it's a training exercise.
Where they would be useful is this sort of case, where you have a simple clearance to pass in a hurry to an aircraft nearby and the frequency is jammed at the critical time.
In other cases of a/c comm failure, nothing to be lost by trying a cellphone.