Perhaps they figured that if they touched the plate and glass but didn't actually eat the sacrifice Jesus made for all men, they would be seen by Christ as refusing the gift of life he has offered them, probably the greatest of blasphemies.
By not touching they could convince themselves they didn't join in the same ceremony Satanists do to insult Jesus, and then when they get home they then hold their own Memorial away from the Elders gauze whereupon they would partake.