Why are technicians (service engineers!) coming out for a simple defrost in the first place? The normal defrost cycle should be automated. For anything else you need someone to come out anyway because something is wrong - there is no point in starting a defrost cycle if the root cause is leaking refrigerant - fix the leak and refill the system both of which need to be done in person.

Because in some ticket tracking system, some customer with the most tickets was nearly always calling for a tech to physically start a defrost. Maybe solving that accounts for 2% of support overhead. It’s best to lose that customer. Second best is telling them defrost is remotely-triggered, and then not doing it. Third best is actually triggering it.