Patch Available - KMS 1.2.274

Actually, I think I know.

The only thing that changes from level 1 to max level of a booster skill is its duration. Same for Soul Arrow, I think.
If they made them passive, they'd have to think up some other way of justifying putting 10 or 20 SP in them. And that's too much work.

Perhaps making them active between levels 1~(max-1), and at max level turn them into passives.