Which decision tree model is used in "standard" random forest? Is that CART? Why not using C5.0 tree?

A perhaps more general question:

Since C5.0 tree frequently have better performance than CART, why people still use CART to build random forest (or people already are doing this)?
My experience is with sklearn and python. 

A Random Forest is a bagging of decision trees, the sklearn package uses a Decision Tree Classifier which is a CART.

You can see in this post that I made a bit ago of how to build a Random Forest tree the exact same as a decision tree.