The gathering/crafting bots are annoying mostly because they drive down prices which makes it harder for people who aren't rich yet to make money and give their owners an unhealthy amount of control over the economy.

Some people also just enjoy making gil for the heck of it, but these players still interfere with that, especially when they're working in tandem with an undercutting bot. I've noticed one on Cactaur that can be seen constantly targeting/untargeting a retainer ball for hours on end as it checks the prices on everything it's selling, and it'll undercut anyone within a few minutes of them trying to sell at a lower price.