Well, the need to take a snapshot--or rather, the activation issue--is described at one point in the license as a "bug". It's a little confusing, but from talking to the maintainer of the VMs on GitHub, it sounds as though they just don't want to dedicate time to "fixing" the activation system. The workaround is to take snapshots. There are actually instructions on the repo for extending the trial without reverting to a snapshot, if I recall correctly, but it's been a while since I've looked into it.