He Wanted to Have The Intentions of the Kohen Gadol:

Sefer Mashmia Yeshua (Ois 397) quotes Rav Moshe Mordechai of Lelov zy"a as saying the following in the name of the Chozeh of Lublin zy"a:

"If Korach had known that he could sit behind the oven and think the thoughts that the Kohen Gadol had when he entered the innermost place on Yom Kippur, he would not have opposed Aharon. His main reason for fighting was because he wanted to merit knowing those thoughts."