If they were really that concerned and it really was that critical, they should have limited it in some way or have been auditing it and issuing warnings before it got to the point of termination. When an employer offers a perk like this, it’s their responsibility to ensure it’s used properly and to monitor its usage, not the employee.

More likely what happened is this was a reason to fire someone they didn’t want anyways. The fact the enforcement is uneven also exposes them to additional liability. It’s likely any one of these employees could sue for wrongful termination, if they were not given a written notice of the proper usage of the perk.