Because it's not really an ability it's a bonus. it's just that having two leaders in your hand cancels the "ability" of the other.
Maybe it does...
maybe it doesn't...
you see, the Leader ability isn't part of the cards you play, unless you play the Leader.
so, the only surefire way to test if the stop ability ability/bonus affects the Leader is if you use Timber, and let him win, to see if he does an extra damage.
but, if you have Timber, and you fight Tank against copper, and copper wins, he will do his damage + Timber's +1 damage.
also, Morphun, and Bridget, their abilities affect at the beginning of a round, and stop ability only occurs while fighting in a round, so they wouldn't have their abilities stopped...
now, this is completely speculation on my part...
but i hope it was at least semi-helpful.
or justified any inconsistencies. (well i still don't know about the Timber thing)
NudeCeleb_LOA: My opponent has Maxed Ambre. He goes first this round, using Ambre. This activates Ambre's Courage ability and gives him +3 power, for a total of 9. I select Striker to fight against Ambre. Striker's bonus is active (-2 opp power, min 1) and he has "Stop Opp Ability". No pillz on Ambre or Striker.
The way it SHOULD work: Ambre's Courage ability is stopped by Striker's ability and Striker's bonus reduces Ambre's power from 6 to 4. Striker wins.
The way it DID work: Ambre's Courage ability was NOT stopped by Striker and Striker lost, 7 to 6.
Leader abilities are not stopped by Stop Opp Ability. And because of this, Morphun is WAY overbalanced in ELO. For 5 stars, you not only get an 8/5, but you also get 3 additional pillz that cannot be stopped by your opponent