The judicial branch is not in the executive or legislative branch. Courts can invalidate laws and regulations from the executive or legislative branches. It is called Checks & Balances. It has kept power distributed for almost 250 years, preventing it from becoming concentrated in any one branch of government. Should that occur, you'd have bad actors enacting a one-party tyrannical state and tens of millions would die, mostly through starvation, but a good many through a state apparatus. It is familiar music. Our civilization has had to deal with such bad actors for a very long time, but despite the lessons of the past, there are still some who desire the one-party state. There is no sign that we, as a species, has completely eliminated the lust for power that's innate in humanity. It is for this reason that the founding fathers hard-coded such things into our nation which act as a stop-gap for tyrants.