For arguments sake let's say the AOE root immunity is 15 seconds, and the timer for the immunity starts when you're rooted. So you have 5 seconds of grabbing your ankles then 10 seconds of running around before the HOX roots you and you go through the same thing until the TOS roots you again as quicksand has a 30 second recast (from memory).
I understand the suggestion (I play a TOS too) but the CCs have immunities based on the rated power of the CC which includes factors of if it's single target or AOE, effect applied etc. IMO if they changed the immunity for quicksand that would effect all AOE roots not just the TOS quicksand. As Zatochi already pointed out, change one immunity you're changing them for all classes to try and keep it fair. (yes I said try because no one will ever think the same way about what is or isn't fair)