It's true they care about film print preservation, but they don't actually do print preservation. They make HD masters (digital tape) from digitally-cleaned up telecine (which is the type of "preservation" they do, a digital clean-up).

HD masters are not a replacement for preserving actual film prints or full restoration.

Their DVD producers do sometimes assist with restoration efforts. But mostly, the film restoration was done by someone else and Criterion handles the digital part for DVD. Criterion was in fact very instrumental in finding the original negative of Grand Illusion.