I mean there's other reasons for why they abstained as mentioned in the edited second part of my post.That's not a reason to abstain. That's the opposite of a reason to abstain.
I can understand why the campaign didn't want the vote to happen today. I can understand why it wasn't the best opportunity to bring this issue forwards (even if I believe it was absolutely right to bring this issue forwards today).
But 'it won't win anyway' isn't a reason to abstain from voting for something you support. Not if the vote is going ahead anyway.
It might cause some people to change their votes because they realise that it can actually succeed.
If the Powell amendment passed the Benn amendment would be sure to pass.
Gives Parliament itself the authority to set the business of the house - rather than the Government.