Roller Derby: why quad rather than inline skates?

[Muffin]

So here I am watching a documentary on the Rat City Roller Girls, wondering why roller derby never progressed from traditional quad roller skates to inline skates.

Are there any actual performance based reasons, or is it just tradition?

[RabbitMage]

I'd guess that part of it is tradition, but skates might provide a better base of support than rollerblades to.

I say this as an out of shape person with weak ankles.

[Muffin]

I wondered about that, but figured that all the extra wheels and soft boots do is put greater stress on the ankles by preventing the foot from maintaining a somewhat similar line as the legs and torso do while leaning through turns.