Mineral oil is much less toxic than DOT, does not absorb water, has higher boiling point.
Bleeding Shimano brakes is almost as easy as unscrewing the caliper bolt and pouring oil into the lever system. On the other hand, for Avid-s one needs to observe strict vacuum.
Why would so many companies bother with an American-specific oil and vacuum-reliant system?
Mineral Oil
Shimano
Magura
Tektro
Gatorbrake
DOT
Hayes
Avid
Formula
Hope