Conferences tend to avoid peak holidays and are rife in September and October - travelling when there is a big conference in town is a pain - hotel rack rates are higher, but also availability is less, in part because conferences buy up rooms on mass for their delegates.

Far fewer people travel on business during July and August (they are taking vacation, their clients are taking vacation, etc etc) so hotels aren't getting the business revenue they might otherwise get (business being likely to pay the higher rates than tourists perhaps?)