Piranha Plants have dozens of appearances to draw from. Off the top of my head,
in Super Mario Odyssey, when they spit stuff at you, their lips form a specific expression that reflects that, and if you knock a rock at them, they'll swallow it and have an animation where they panic a bit.
That's already way more personality than Steve has.
On most other characters, that kind of stuff would work, absolutely. The issue with Steve is that his animations are limited; he can't bend his elbows or knees. His arms and legs are like an action figure without elbow and knee joints. Sakurai could make the executive decision and give him elbow and knee joints to allow some extra mobility and expression, but then that wouldn't be faithful to the animations of the original game.
So eating something would just have the item spawn in his hand, he'd rotate his arm a little bit to kind of raise it to his head, the item would disappear into thin air, and then he'd rotate his arm back down.
Compare that to Young Link who pulls out a bottle of milk, displays it for a moment, chugs it, wipes his mouth with his forearm, then gives a smirk.
That's the issue I'm trying to convey. Either Sakurai has to change the character in order to make him work, because his animations are so limited, or he sticks to those limitations and we wind up with a character that's rather boring.