the core surely is anti-commercial but the main subreddits like r/funny or r/pics and the like are so huge that the majority consists of "normal" internet-consumers that visit other sites as well and are used to commercials, the reddit-frontpage is mainstream, it's no longer an obscure site that some nerds know about

and in addition they could have very targeted advertising for the highly specialised subreddits.

but aggressive money-making surely would destroy the community and turn the site into a superficial link-collection with comments in the style of youtube but you could milk it for a couple of years and earn a lot