Blizzard has consistently tried to nerf combo and aggro decks and tried to buff control decks since the beginning of forever and it hasn't stopped the mass aggro from dominating. Leeroy is the single most influential card in the entire game for making aggro and combo as powerful as they are.
He has eaten enough of our chicken. Get rid of him please.
I agree I was really surprised to see that he remained untouched since he is a vital part of OTK combos. But considering that he's mostly played in Warlock (in combo with PO and Faceless), they probably went with PO since it's played in almost all Warlock decks.
He's a 5 mana neutral fireball that gets stopped by taunt. I don't think he's a problem.
Except that Fireballs can't be buffed by Cold Blood, copied by Faceless, etc, etc.
Fireball can be used as a desperation board control play, for less mana. Leeroy is next to useless for that. It's 5 mana for 6 damage. Emperor is also rotating out and leeroy has already been nerfed. Don't get me wrong, I don't even own the card, but you might as well start asking for wolfrider to be moved too.
Leeroy is a finisher, primarily. When you concede when you see him it's because you have mathematically lost by that point anyway. He's far from a critical card in most aggro decks, let alone a must-have. I hardly ever see him anymore, as most good aggro decks don't need him to finish you off quickly.
And long and short of it, that's why he's not going to HoF.