Chelsea Manning stood trial. Edward Snowden did not.
Not that there is no precedent of course (Nixon).
There is no extradition request to the U.S., so when fighting an extradition to U.S., Snowden is beating a straw man.
Commutation is reduction of sentence, it can only happen after conviction.
> Like 97% of the cases that go to prosecution in this country, let him plea to a lesser crime
Is there any indication that Snowden has any interest in pleading guilty to anything?
Pre-emptively pardoning Snowden before he spends a day in prison sends the signal that the government isn't going to punish people for leaking, so go right ahead.
Commuting Manning's sentence after seven years still leaves a pretty harsh warning for future leakers (is leaking that information worth seven years of your life?) while showing a degree of mercy to the individual (I mean, not the degree of mercy that commuting after 2 or 3 or 6 years would be...).
Regardless of what you think Obama's secret inner beliefs and motivations are, I think it is reasonable to assume that as Commander in Chief and President of the United States he wants the people he entrusts with secrets to keep keeping them.