Yeah and i've wasted all my money on a flat and garage I'm never going to use. The cars you are allowed to put a tracker on are all shit.
It is annoying, you can't store or modify them and they seem to attract more cops than normal. These cars cost hundreds of thousands to buy so it seems that they did it because if you could just steal them nobody would ever buy them and I guess they're one of the main things to save for. So either it's to keep the chase going a bit longer or (and I really hate to accuse anyone of anything like this, it's more DM's area) they couldn't undermine their economy because they sell cash shortcuts.
Found another sports car last night in freeroam and had a load of cash so went to buy a garage to put it in. You aren't even allowed to keep them there. It tells you to buy the good cars on the games internet like the chop shops do. That is seriously retarded for a GTA game.