I just noticed how few non-terminal Attack cards there are. This makes sense, of course—repeatedly attacking your opponent can be very strong and very annoying. Having Attack cards be mostly terminal makes it that much harder to just load your deck up with Attack cards so you can Attack every turn; to do that you need to either also invest in a lot of villages or run the risk of your terminals colliding.
So what are the exceptions?
Sir Bailey and Dame Molly—these are only 2 out of 10 Knights, so you can't load your deck with them
Familiar—has a Potion cost so you can't get a lot of them fast
Urchin—a very weak attack
Spy—a fairly weak attack, especially if not stacked
Scrying Pool—has a Potion cost and the fairly weak Spy attack
...and what does that leave?
Minion. The only non-terminal Attack that (a) is relatively easy to stuff your deck with and (b) reliably has a decently-strong effect on the opponent (discard-5-draw-4 is probably on average at least as effective as Margrave, and it's idempotent rather than weakened by repetition). So no wonder people find Minion annoying to play against—not just because it's disappointing to discard your hand, but because it's the only card that makes it really easy to very reliably hit with an attack of pretty decent strength.