IMHO. . .
Yakult's bottle is the required daily dose of it.
Too much of something would do more harm than good.
They keep it in individual packages so that it can be consumed right-away once opened.
Since it contains live micro-organisms, the contents needs to be consumed once opened.
Resealable caps would decrease its potency thus impacting its quality.
I think, the locally-made Lactopafi has the same aim as Yakult but far-off when it comes to taste.