Because you are not going to find a PMC3-XP processor, and if you do it won't be compatible with the newer Crestron products. The benefit is having a future proof system which is what you said you wanted. Prodigy is not a future proof solution since it has been discontinued.

Here is a solution for you.
Keep your prodigy system (I am assuming you have an iPad/iPhone app for lights, Audio and Climate). Add a MC3 and HR100/150 remote to only do your home theatre (you can use the same Crestron Mobile app to control your home theatre, its just a different connection). As time goes on slowly migrate your prodigy equipment into Crestron products until you have eliminated your Prodigy parts. As time goes on the MC3 will still be a current processor and allow for newer devices to connect to it when they are released.