Originally Posted by
sjmcc13
Because it is no where near as good as lackey.
Lackey comes down on turn 1, so when it swings on turn 2 you normally only need to worry about 1 blocker if any, and goblins does run some removal so it can kill a 1 drop often enough. with instigator it does not swing until turn 3, so there are likely multiple blockers, and you need something to make it unblockable as they will not let it through.
You will still run it in Modern, but it is no where near as good as lackey.