One key factor was the difference in musical styles. Slipknot is known for its heavy, aggressive sound, while Limp Bizkit's music is more rap-oriented. This stylistic difference led to a lot of criticism from both sides, with each band accusing the other of being derivative or lacking in originality.
Another factor was the bands' respective popularity. Slipknot gained a large following in the late 1990s, thanks in part to their controversial image and sound. Limp Bizkit also achieved mainstream success during this time, but they were often seen as a more commercial and accessible band. This difference in popularity led to a lot of resentment from Slipknot, who felt that Limp Bizkit was not as deserving of their success.
Finally, there were several personal conflicts between the members of the two bands. In particular, Slipknot frontman Corey Taylor has been outspoken in his criticism of Limp Bizkit frontman Fred Durst. Taylor has accused Durst of being a sell-out and a fraud, and has repeatedly made disparaging remarks about his music and personal life.
All of these factors contributed to the conflict between Slipknot and Limp Bizkit. While the two bands have never engaged in any physical altercations, their rivalry has been well-documented and has lasted for over two decades.