eh.. Why do manufacturers speak mAh instead of watts??

people get very annoyed when they know what that really means. Say for example, every power bank available says 10,000 mAh, or 20,000 mAh (or whatever), but all those are at 3.6 volts (not at 5 volts). As most of the other specs is in 5 volts, most people don't even know this.