I believe "it" happened after the release of skill capes. Before this, one would have 99 in skills that one enjoyed. After the release of skill capes, 99s were a measure of "power" or a way to determine the better player. Players started wanting 99s in as many skills as they could attain and "buyable" skills were the main targets. Skills such as: Cooking achieved less profits. Now fast forward a bit and there is more and more players all the time. Most buyable skills were still making profits but the profits were diminishing. Still there was much profit. Finally the grand exchange is thrown into the picture. Players now used the grand exchange to simplify the process of obtaining items for 99s. Nowadays to achieve a 99 is a simple process: 1.I want 99 cooking 2. buys 60k sharks 3. Grindfest All in all, skilling became non-profiitable when everything became easier: grand exchange, cook x etc.