maybe because if you send a S / T card you are indirectly increasing the atk, following the same logic it works with RESD as well. But i really don't know the answer
When I attacked into a brave Neos, there was a Neos Fusion in the GY. I had Spirit prepared to negate, but I wasn't prompted to activate the negate even though he did banish NF to protect BN from destruction.
His life points went to zero during the attack also, but I still expected the game to ask me if I wanted to negate or not the NF.
When I read the text I don't see why it would be passive instead of active when it says "when ... you can ..." and not "all destruction are negated at anytime" type of text.
Spirit Dragon can only negate the activation of a CARD while Dark cavalry can negate the activation of a card's EFFECT as well. That's the only correct answer here and it has nothing to do with IF or WHEN.
They should write the ruling that way for beginners to understand.
So, Neos's fusion says "you can banish this card from your GY instead." but doesn't exactly talk about an effect like "negate the destruction". So no after-cost-effect to negate.
LoL.