From the FAQ:
Can I login into Google apps (Youtube for eg)?
Despite all our efforts to communicate with Google, we can’t make our PicoPix Max to be certified and get the GMS so we cannot have the Android Playstore. But you can use your own account on Youtube!
In other words, you need to ask Google why they chose to not certify the projector for Google Mobile Services (GMS).
As for your question about casting: have you tried the steps outlined in this forum post?