I'm not saying bolvar would be bad, but skeleton knight just fills a different role. And I'd imagine bolvar works best when you run small minions played from cards, not just hero power.
I can tell you from experience that bolvar does not work best when you run small minions played from cards. Aggro decks aren't really looking to throw their minions away all that quickly so you actually don't gain attack for Bolvar that much more quickly anyway. Bolvar works in greedy control paladin lists because it represents a huge stat threat that control decks have to expend their premium removal and silence cards on, which enables you to play other large minions with less concern. Bolvar can eat a BGH so you can play Dr. Boom or Ragnaros. Bolvar will eat a silence so you can play Sylvanas, Tirion, or Piloted Sky Golem (another card better than Skeleton Knight). Bolvar gains attack much faster than people theorycrafted because the hero power gives you a consistent source of minions.
If you are playing a greedy control paladin deck, your aim is to counter other decks with large minions in them, like Handlock or Control Warrior. If you play Skeleton Knight against those decks you are giving them a gift, because they have plenty of options to remove Skeleton Knight with minimal resources and you are much more likely to lose the Joust. Bolvar is much harder to remove and is a much greater threat. Why would I play a 7/4 when I can play a 10/7 instead? Heck he's probably even better now with Justicar Trueheart in the game.
The meta is in the completely opposite direction of where Bolvar is as a card, which is the reason he doesn't see more play.
