* Players cannot dismiss or add party members while undertaking exploratory missions.

[Zojha]

I feel like most deicsions that SE makes are based on the idea that all players are "kind".

I reckon this decision could also well be made because they assume that players won't be "kind".

In particular, they might be anticipating a larger amount of premades in airship exploration and thus a larger degree of premade votekick abuse. That's really just a guess, though.
Maybe it's also just SE trying to give us a broad hint that this feature is intended to be done within FCs.