ALPA negotiated contracts commonly have a statement in them to the effect of:

"A pilot will only be required to perform those duties directly related to his certification or training as an airline pilot."

Making a gate PA has nothing to do with being an airline pilot other than the fact that they want it to be a pilot doing it. That is a customer service function that does not occur in an aircraft.

If this line is in your contract, thats why you have to put the gear down even though you're not contractually obligated to. If its not in your contract... well... enjoy making those PAs. haha.