The same reason that Ron Paul won all of the Republican debates in 08 and 12 but was never credited for it.
People who have true passions and beliefs are so often .. well.. ignored.
The mainstream wants who they want.
And they don’t want Bernie, the same as they didn’t want Ron Paul.
The true match made in heaven for America would actually be the libertarian free wheeling Paul vs the man of the people socialist Sanders. That, really, would be a ‘choice’ ..