We're not close enough to the rotating knives of Brexit Day.
Give it another few weeks of companies leaving every day, warnings from major industry figures, etc. and the mood in Parliament will change.
Right now, there aren't enough MPs willing to vote for a second referendum for it to pass. But once we can feel the wind from the blade tips as they swish past, waiting to chop us up on Brexit day, sensible MPs will come around.
Assuming we haven't reached a deal they can sign off on by then, and we haven't extended Article 50 to move Brexit day, the next spoke to throw in the wheel of a no deal outcome is a second referendum. So the pressure will be phenomenal for MPs to fall in behind the idea and support it.