>>Why is anybody in the government so unable to provide convincing evidence that the Russians were directly involved in hacking the DNC?
Russia has plausible deniability. US intelligence community simply doesn't find it very plausible.
At the end of the day, it comes down to the saying: if it walks like a duck, and quacks like a duck, it's probably a duck.
What we know for a fact so far:
-Trump has very strong business and personal ties to Russia
-The DNC has been directly targeted by actors with known ties to Russian leadership (but not a state actor, because Russia wants plausible deniability)
- Russian leadership is celebrating the fact that Trump won
- Donald Trump is STILL refusing to release his tax returns
- Donald Trump keeps disparaging the entire intelligence community for trying to delegitimize his election, despite having applauded Comey's smearing of Clinton two weeks before the election
Based on these, it's reasonable to conclude that something very fishy is going on.