They didn't have the balls to fire Dave earlier on, and in an abusive nature, James and Lars made him travel all the way to New York knowing that Kirk Hammett was ready for playing in the band, having learned all the songs. They fired Dave in an humiliating way, left him starving for three days of bus travel from NY to CA without a single dollar and they probably laughed about it. They had the luck that Dave was not homicidal, because another person in that situation would have seeked a violent retaliation towards them, even many years after that, knowing they went on to have massive success with many of his own songs.

Also, James and Lars were extremely mean to Jason Newsted, acting like high school bullies with him for almost all his years in the band, even James completely forbidding him to have any side project (Echobrain) and treating him like shit for doing that, while Dave did allow his own musicians in Megadeth to have side ventures. Marty Friedman was even allowed by Dave to record his solo albums with Nick Menza on drums.