Rush is a dreadful sound to a cultured ear. Abrasive in the extreme.
Floyd was a ever evolving band that became more melodic and smoother in time to the point of eliminating any abrasiveness completely from their sound.
First impressions of Rush nearly 50 years ago was laughter at the sound and smashing the LP, never to be heard again for decades until visiting the US where they were/are a local identity.
Floyd's beginning was in a time of avantgarde allowances in music where "underground" was "cool" so fit a market segment that was there, but not mainstream. It evolved in the 70's to attract larger global audiences.
Looked up a site called Best Selling Albums and according to their figures Rush sold
Canada - 28 LP's = 2,543,001
UK - 12 LP's = 840,000
US - 28 LP's =24.083.334
Floyd sold 250 million and Dark Side sold 50 Million alone.
The market apparently agrees with me.