Dust seals are actually better called corrosion seals

If the caliper is aluminium and the piston is stainless steel then there is nothing to corrode so the seal isnt needed.

They came about due to the mass production of mild steel chromed pistons in cast iron calipers which after a while begin to rust and will stick. This seal helped to prevent the rust forming.

What are the pistons made of ?

If your brakes are that dusty that you need to clean them every month then your on the wrong pad compound and could do with changing to a lower dust emitting one