why does the group loot table thing work like that?

like i want a couple pre-set groups of items and you roll one of them, for example like theres 4 groups, like one with 5 splash potions, one with like 7 axes, one with like 1 sword and 3 snowball stacks and one with like 3 stacks of acacia logs or something, and then you get like one of the groups, like without them mixing, like you get either the one with the 5 splash potions or the one with 7 axes and so on idk i might be dumb but it just doesnt work like that for some reason