Tactically speaking, I don't blame him. He is ahead in the polls, and the flack from not having the balls to face Andrew Neil is likely to be less than the flack he would get after being torn to pieces by him.
The Tories probably reason that the more Corbyn is in front of the cameras, and the less Boris is in front of them, the better their results are likely to be.
Fully agree, Corbyn has done them a favour by going on and getting grilled/exposed for what he is.
He has gifted the Tories with negative press against Liebour and because Boris has done QT and other interviews he is insulated against the 'not doing interviews' that May got hammered for.
Why chance it? He is ahead in polls and has everything to loose and little to gain. So a good tactical move and I don't blame him either. Not a coward, far from it. Clever tactics.