Mac and Dennis' house in the suburbs

The room is more than likely like that because Mac and Dennis are used to living in the city, in an apartment building.

When living in an apartment things like trash collection and pick-up are handled by the building and not the responsibility of individual tenants. Tenants of an apartment building normally use things like a trash-chute or a dumpster to dispose of their refuse throughout the week. So they don't have to remember what day the collection happens.

However in the suburbs homeowners are responsible for remembering and utilizing their designated trash collection days to place their garbage out on the curb so that it may be collected on that specific day.

Mac was responsible for the day-to-day tasks around the house so two things could have happened:

1. Accustomed to just utilizing a dumpster or trash-chute when living in the city, he didn't know how trash worked in the suburbs. So decided to allocate a room for garbage and just figured he would 'deal with it later.'

2. While aware of the designated day for trash collection, Mac simply forgot and therefore missed it. This happening multiple times over a month, resulted in a large cache of garbage bags.

As for the air fresheners-- Garbage stinks, and a lot of garbage stinks a lot. Not wanting Dennis to discover his mistake, he used air fresheners to cover the smell.