The idea here is to provide a better experience (and equal or better prices) for people who might otherwise sell to trolls. such a term on the transfer would do nothing to enhance the attractiveness of the program to the people Google is looking to do business with (whether or not that's how Google is likely to use the patents), and people who would be motivated to participate by such a term aren't people who otherwise would be likely to sell to trolls, so there is no real reason for such term.

Google might subsequently make such a pledge for particular patents it purchases -- or submit them to reciprocal licensing pools, which such a pledge might conflict with or reduce the utility of -- but that's separate from the purchase terms, and there is no good reason to tie them together.