Russians hacked the DNC?

I'm hearing on NPR, Fox, and the 'Net a theory that the Russians hacked the DNC emails and released them on Wikileaks to help The Donald.
Why in the world would they do that?
    Hillary is a known quantity.  She is not very smart, she can be bought, she won't make waves.  She has had four years as Secretary of State to demonstrate her incompetence in foreign affairs.  If I was Putin, that's exactly the kind of person I would like as president of the only surviving superpower. 
   Trump on the other hand, might do anything.  America is an exceptional country, and with imaginative leadership it can do almost anything.  Under mediocre leadership (Hillary) nothing much will happen.  But under charismatic leadership America won WWII, developed nuclear weapons, traveled to the Moon, eliminated polio, and gave its people the best standard of living in the world.  Under Trump, America could be an irresistible adversary to Russian expansion worldwide.  Why risk that?  Far better to have a mediocrity who will let things slide as they have been doing.   
   So I don't believe the Russians wanted to help Trump.