It's because SE put even the basic actions as a server > server interaction
This is all about control. By having everything server side it can't be modified by outside parties. Means everything has to work off of the screen. Bots actually have to move the mouse and click the mob as opposed to just sending the server a message that mob 23316 has been targeted. Fish bots actually have to fight the mob using the mini game instead of just sending the "I Win" command to the server.
They're trying to prevent the economic problems bots created in XI, but they're doing it in an *** backwards way. No AH means bots can't effectively undercut everyone on the server, corner a market, or mass produce items with AH materials. Client side interface means all bot actions have to be done visually, which is much slower and more difficult to program. FFXIApp couldn't be created for this game, for example. Note they took the legal route against Windower because nothing they can program could prevent that.
They're the SONY of the software world, it's their way or no way and it's going to bite them in the ***.