They can also add affiliate links and make some good profit or sell their own products (trading tips, coatching...)
Doesn't apply to new websites. Where are they going to get their exposure from? Surely paid advertising comes into play unless they're some big shot on social media.
Op didn't mention the site was new. so i assumed the site already has quality content and qualified traffic. Otherwise, i think it will be very hard to monetise a site without those two items.