Main reason for that is what in my opinion a rather stupid philosophy. When ive spoke to Americans, the answer i get is that exposed wheels "improves manoeuvrability". i have asked how having your wheels fall off achieves this, so far havnt had a decent answer.

The only real answer i can think of for this is that when your on your side (ie stuck on a wedge) you can drive off it. However the more people i talk to about this the more it sounds like a convention they have gotten into and refuse to change from (such as how they activate robots).

Other answers ive had is that if you cover your wheels, then the armour can get bent and lock the wheel - ignoring the fact the blow which locks the wheels, probably would have torn the wheel clean off aswell. Another one ive heard is that by removing weight around your wheels you can increase the weight of your weapon.