Generally speaking, I order twenty to thirty 10ml vials of Test each time that I order Test for the mere fact that Test is a base and thus heavily used substance, and because I receive a substantial discount.
So let us suppose that two or three of those vials break while in transit, thereby necessitating that my supplier replace those two or three vials, which my supplier will do - no big deal. But if my supplier were to mail one 200ml bottle or one 300ml bottle, not only would I likely become the target of a controlled delivery in the event that that one gigantic vial were to break (imagine the mess), so too would my supplier lose far more money relative to their having to replace my gear.
Ergo, if it made sense to produce 200ml and 300ml vials of juice, then labs would do that. But that wouldn't make sense. So labs don't do that. Simple.