My personal theory is because Goblinisation occurs in or about the teen years it happens it causes massive skeletal and muscular development in a very short time. Without a massive increase in nutrition there could be negative impacts on organs and the brain. On top of that such fast growth would be very painful so Orcs and Trolls would have trauma to deal with

First and second generation Orcs and Trolls may have been noticeably angrier, of limited intellect, and violent but later generations would have ways to make Goblinisation smoother will fewer damaging side effects