Follow the money, this isn’t totally about volunteers. Phoenix Comicon is a for profit convention. They are attempting to avoid a massive lawsuit (a la Emerald City) due to making money off of a completely volunteer force, many of whom offer specialized services which fall outside the scope of a general volunteer…

for non-profit events, that makes sense. For profit events have an entirely different structure with volunteers, and a ton of problems. It’s likely just flat illegal what cons are doing with volunteers if they are for profit cons. See the case with Emerald City Comiccon

I feel like this will make volunteers less likely to work as now they have paid a fee to gain admittance, not sure what the standard entrance fee to this event is but for $20 you gain access to places reserved for staff on top of access to the event so for the low, low price of $20 they created a VIP pass.