It's not just with Lockjaw. It happens also with Leech, Aero, or any other Pool 3 card that causes issues. And I think the key words here are "Pool" and "three". I've seen more people saying that MODOK (a super fair and balanced card that wasn't meta defining at all) deserved a nerf, than people saying for example that maybe Lockjaw could use a slight adjustment since it's his ability what makes Leech feel more frustrating (Leech is an unfun card, yes, but it has the big downside of being available only in turn 5, but with Lockjaw it can be played before).

The mantra seems to be that it's ok that some Pool 3 cards can completely mess up your opponent (Aero, Leech) or allow crazy plays on turn 6 (Wave); but if that same crazy ability exists on a Pool 5 card, it's the end of the world, even if the card has counterplay (best example here being Galactus, you'll see people complaining about him even tho he HAS counters, and not to mention it's usually a super telegraphed deck).