In fairness, they can’t just pop down to the hardware store and use one of those soap dispensers, since the changes in air pressure at altitude would cause them to leak all their contents or pop.
The average dispenser is basically two one-way valves, and a flexible tube you compress to squeeze it out (or a bottle with a pump). Everything inside would be forced out by the lower air pressure.
Planes don’t maintain sea-level atmospheric pressure the whole time. That’s why your ears pop in-flight.