Pyston has a goal of full C-API compatibility, unlike PyPy. Dropbox are almost certainly not trying to create the greatest benefit for the community, but rather

Pyston has a goal of full C-API compatibility, unlike PyPy. Dropbox are almost certainly not trying to create the greatest benefit for the community, but rather the greatest benefit for themselves, and they have huge amounts of Python 2 code in production. As such, Python 2.7 with full C-API compatibility makes sense for them to focus on.