A and C, while I admire you for offering this to crew, it might not be so much that they don't take you up on the offer rather than that they simply can't because they don't get a chance.
Another likely reason is that we tend to take our break at the same time and the team "spirit" carries through this and we like to eat as a group.
As for legislation, it's all a bit grey at the moment, but if you have a Union recognised then get them on the case. At Britannia (ok, tfly) we are quite happy to (and have done so when required) to drop a service to ensure that the crew get an oppertunity to sit down for a half an hour and get some food in them at some point in the day. Management have no comeback. Perhaps something to look into threatening your companies with.