Why should Juries have more discretion?

The bureaucrat is not free to aim at improvement. He is bound to obey rules and regulations established by a superior body. He has no right to embark upon innovations if his superiors do not approve of them. His duty and his virtue is to be obedient. -Mises

Because the judges don’t have enough! From the law.com article:

If it made Robert Bryan "sad and a little angry" that federal sentencing guidelines in the 1990s forced him to impose draconian prison terms on two drug defendants, one can only imagine how the Seattle federal judge feels now.

The 9th U.S. Circuit Court of Appeals vindicated his sentiments in December when a three-judge panel granted his 2005 request to let him reconsider the two jail terms, citing Bryan's courtroom expressions of dismay. The judge had filed his order because the 2005 U.S. Supreme Court case U.S. v. Booker, 543 U.S. 220, had made the sentencing guidelines optional.

But this didn’t apply retroactively to the case unless "extraordinary circumstances" existed. That draconian sentences were imposed based on unconstitutional guidelines is not an “extraordinary circumstance” is an assault on reason. Clearly the politicos don’t care about justice so the juries must.