After Musk renamed his X account, the New York Post published a post analyzing the reasons for the name change. In response, Musk retweeted the post and replied with "Kek" to express his approval.
In fact, the reasons for Musk's name change are not complicated; either it's to promote the virtual currency Kekius or because he likes the game Path of Exile 2.
Apart from that, there is no more reasonable explanation. Of course, the specific reason still needs to be clarified by Musk himself, and others' analyses are merely speculation.