Couple of reasons:-
1. Trouble with GPS is that it needs to be able to "see" the satelites to determine it's position, which limits the places it can be "hidden".In that daily mail article it was attached to the victims towbar, which must have taken her all of 30 seconds to discover. Toyota IQs don't have a towbar - you can't really tow a lot with a 998cc engine - so it'd take even the thickest weasel less time than that to discover something "hidden" on the roof!
2. I suspect that one of those devices might cost a bit more than a tank full of fuel for a bike, to be permanently losing them to the Council every time you deploy them might end up being a bit expensive.
3. It's probably Illegal, since we don't have RIPA ot DPA Authorization to use them.