Oof..me neither. Although I can safely claim doddering age and decrepitation of the memory on my part, seeing as how it has been at least 35 years since I last watched M:I. Yanno, if neither of us can remember him, clearly he was not important enough to be remembered. So there.

(A) Jackboots were the obvious signal, like black hats on bad cowboys (and thus George Lucas' stunning display of transversion -- nay, subversion of the ideal in Star Wars, where the good guys wore black..but I digress). Who else wears the darned things? I suspect no one likes to wear jackboots because they are supremely uncomfortable, and make the wearers rather irritated, and prone to engaging in acts of torture just to take their minds off their discomfort. In my opinion. I've never worn jackboots, although I have worn engineer's boots.

So.

(B) Thugs -- as we all know -- are of little brain, and cannot understand that wearing jackboots is the source of their pain and bad mood, so they keep on wearing 'em.

(C) Finally, the prop department bought lots and lots of jackboots, and all the bad guys had to wear them. It was in the contract.

Pick one. Any one you like. It's bound to be at least somewhat correct. ;-)