@Sekuru Dhorofiya audio mixing is more challenging because of the number of decisions you have to make on a given song, plus the number of people you have to answer to e.g. band members arguing about the sound of a kick drum, lead guitar, the level of vocals on the chorus (or hook), etc the list goes on and on it's endless.
I am not saying mastering music is easy, but it's a process (or the final stage) that doesn't necessarily involve a lot of people skills, and also there isn't too much technical stuff to be done to a decent mix. It's either you have good taste or you don't. If you have bad taste you will ruin something that already sounds like a finished record and just needs more level i.e.,
brickwall limiting (or...