It complicates the many checks done by both external mods and other galore mods. Imagine you want to do something as simple as making it so all sciences are made in a different machine; in your proposal, the mod dev (or another Galore mod) would need to replace three categories (but only when AAI is loaded). Not to mention how some mods just do not handle recipes with weird categories at all and could crash.
(Not very hypothetical; implementing it like that would break the Maraxsis compat.)
Alone, these kinds of things aren't that big, but they add up fast, slowing down testing and releases. In order to keep maintaining such a mod suite I must minimize these things, especially if the issue I'm trying to fix lies with another mod. I'll make an AAI bug report tomorrow.