I get what you mean, tho it can then be confusing when you want to add it to a new one: the name is already pre-filled, the type of the model is greyed out (as it's already set for the existing model), and it's not entirely obvious to simply specify a different name for a new model. the current dialog offers both: you type a new name if you want a new model, or select the existing one (type the first character will do, followed by Enter).
Solving the confusion would then require a 'new' button which is redundant too.
So it's a mixed bag: a change as you suggest is helpful, but not helpful for a different situation... we'll think about it though.