When a creature has the flying ability, that means it cant be blocked by most other creatures
After all, there's a reason that the power nine includes six cards that produce colored mana for free
Counterspells in general can feel pretty bad for the player affected, and theres a political tension in how much bullying you can get away with
More fodder for repeated card draw in that Glissa deck or however else you want to recur it, plus a little mana fixing on the side
Ethan Fleischers design team hit on the great idea of reusing the Unearth mechanic on a lot of Necron creatures, letting them rise from their tomb world (uh, graveyard) to ambush your opponents
But if that were the case, why not just go for Slither Wings more common variant -which is sitting at less than a dollar- for testing