Why someone buy gil on illegal sites?
The reasons vary widely, but do you know the harm of this practice?
Many servers are filled with bots taking up the space that a player could have without having to be in huge queues to get in the game. Restrictions on new character creation and transfers could be lifted if not for so many bots created.
Not to mention the economics of the game. The gil that you buy from illegal sites is generated by bots who repeatedly get dropped items and resources and sell them on the Market Board for ridiculously low prices. This pulls the prices of those items down, disrupting the profit of those trying to make money via drops.
FFXIV is not a difficult game to make money. It takes a while to learn the many possible ways to make a profit, but once learned, the formula can always be used. We have gathering and crafting professions capable of generating good profits. Palace of the Dead, weekly quests, roulettes and many other ways complement the profits without much effort or time within the game.
So why bother to buy something illegally? If this hurts the server the most, why do it?
You be at risk to be banned or hacked and get some viruses on your PC, also.
As long as there are people buying gil illegally there will be bots disrupting the economy and the server population harming everyone. If there were no people willing to buy gil on illegal sites, bot makers would lose motivation to hinder us by diverting resources that could be used by SE to make the game safer and more fun for all of us.