Stall pretty much died in Gen 4, not Gen 5.
I think we can all agree that the Ape is responsible for single handedly destroying the seemingly "impeccable" SkarmBliss core. Which is why the two saw a DRASTIC decrease in usage in the 4th and 5th generation. The Ferrocent core was created, and for a while many thought it would counter Infernape. However, an Iron Fist boosted Infernape with Life Orb, Close Combat, and ThunderPunch (Yes, people use this set. It's on Smogon, actually.) Gave the core a run for it's money.
It is true that since the core of SkarmBliss has fallen, the usage of Infernape has fallen as well. But with all these Mixed-Attackers running around this generation, (Namely Hydreigon, Mix-Mence, Jirachi, need I go on?) It seems almost useless for stall to even exist. People argue that Hydreigon, and Infernape are barely seen in standard play, but they still exist. It's a simple fact. In a meta-game full of unpredictability, you must be prepared for anything.
Lastly, Stall NEEDS hazard entries to work. Starmie laughs at toxic spikes, and can retaliate with a LO move due to it's versatility. Donphan takes minimal damage from stealth rock, and can always switch on the offensive. And Roar still exists, people. Did I mention that Dragon Teams completely destroy stall? Magnezone KO's any steel if it can manage to trap it, and Haxorus and Kyurem-B have become infamous for their ability to 2HKO nearly pokemon in the game.
All in all, stall is dying. And for good reason. No one likes to lose, and there's no reason to use a full blown stall team in a meta-game full of hard hitting pokemon.