The decision to use butter was made for texture before it was made for anything else. Butter is around eighty percent fat and sixteen percent water, and that water turns to steam in the oven. In a cookie this small, that steam is what separates a snap from a crumble.
Liquid seed oils bring fat without the water and without the milk solids. They produce a softer, flatter cookie that never develops an edge. We tried it. It was not the product we wanted to put on a shelf.
What the milk solids do
Butter's milk solids brown during the bake, and browning is flavor. In a formula carrying as little as three grams of sugar per serving, we cannot rely on caramelizing sugar to build depth — so browning milk solids and agave do that work instead.
This is also why the bake window is narrow. There is less sugar buffering the process, so the margin between properly browned and overdone is smaller than it would be in a conventional cookie.
The tradeoff is stated on the pack: every Sweet Logic specimen contains milk, and none of them are vegan. That is a direct consequence of a formulation choice we would make again.