Man has received free choice and can do with it what he wants. He also has received the authority to regulate the world or to foresee it with rules and regulations to have order and no chaos.
But the Bore (Creator God) does not need your mitzvahs. God desires your mitzvahs.
There is no why.
If there would be a reason why, it would not be a true desire.
If there would be a reason why, then the mitzvah would be no more than a means to an end, like a disposable utensil or a paper napkin.
But a mitzvah is a jewel of immeasurable value, the embodiment of divine desire.
And so the sages taught,
“The greatest reward of a mitzvah is the mitzvah itself.”