This has been discussed many, many times before. We ban Pokemon, not Pokemon + ability combinations. Firstly, the reason is that a Pokemon is made up of all of its components, and banning certain parts of it to nerf it would just get ridiculous once you think about all the different Pokemon. Can you imagine our tiers to be stuff like "Kyogre can't use Water attacks, Groudon can't use Rock Polish and Swords Dance, Dialga can't use Draco attacks", that list would go on forever. For the sake of simplicity and consistency, we just ban Blaziken outright. The Drizzle + Swift Swim ban is a bit different, because Aldaron's proposal was used to stop more bans from happening at the time (rain gets banned, sand would probably follow, then sun). We're all about minimising the number of bans.
As for Speed Boost Blaziken himself, he was just too good of a sweeper to stay in OU.
Furai i rule f****s
20:09 Melee_Mewtwo wow
20:09 Melee_Mewtwo the furry is lord of the gays