It wasn't boosted because there was no easy way to boost it's droprate without having some impact on the drop-table for the main-game even if it was a marginal one because of the way an elixir is chosen to be rolled as part of the normal loot table instead as it's own separate roll which has to be cleared first like the sigils.
I could have made a second table just for leagues for the corp but that honestly felt like a really messy approach, I was aiming to make a droprate increasing system that was much more elegant than just copy pasting the same thing twice and changing a few numbers.
I know that' not your concern though, I know you probably don't care about how it's coded you just want to get what you're going for but at least this is hopefully some insight as to why even if you don't agree.
Good luck on the elixir hunt! You've still got a ton of time left this League to get them :)