There are many reasons. Chief amongst these are:
a.) dirt carried by snowmelt will over time reduce the drainage capacity of floor drains and eventually clog them resulting in costly cleaning by a vacuum truck and even possible repairs;
b.) the dirt found in parkades is considered “contaminated” by the Province of Alberta and prolonged exposure to the dust is known to be unhealthy;
c.) by their nature parkades are very dry environments and the moist dirt brought in by vehicles quickly looses it’s moisture allowing dust to be stirred up from the movement of vehicles (or even pedestrians) which will coat everything in the parkade and cause gas, fire and other sensors to malfunction over time or in extreme cases, prematurely set off an alarm or fail completely.
This dust is also very hard on the air makeup unit, garage door opener and elevator components requiring more service calls and in excessively dirty parkades, is tracked throughout the building increasing janitorial expenses and significantly reduces the lifespan of carpets;
d.) dirt and gravel will wear down water protecting membranes on multi tiered parkades requiring high repair or replacement costs. Many buildings that are multi levelled with a membrane are even cleaned monthly during the winter depending on vehicle traffic.