To turn the melted components into a metallic glass, rapid cooling is necessary to achieve the atomic structure (random) desired.
The problem for larger pieces at this point is that it cannot be cooled quickly enough to make it into a metallic glass, thus the issue of size.
Additionally, it is rather expensive still so there may be some push back against the price for bigger, bulkier parts at this time in many industries that could otherwise benefit from the technology at this point in time.