TLG Chart, page-18

I would think that it comes down to TLG's business model in being a technologies company and not merely a producer. But consider also that the company needs to liberate the graphene from the graphite first before it sells it to users of graphite. The long play here is the graphene and the technologies that it can be used for. If the company started mining the graphite and selling it, it would surely be shortchanging itself here.
I won't speak of any kind of 'use by date' for the graphene (if any) but I'd assume that storing it for extended periods of time may reduce its usefulness, plus the company would need to take on the burden of the additional costs to store it.