Would it even be feasible to monetize Tumblr by running ads on massive scale? I would assume one reason for its popularity is the lack of ads. This has for exam

Would it even be feasible to monetize Tumblr by running ads on massive scale? I would assume one reason for its popularity is the lack of ads. This has for example allowed quite relaxed page templates, you can make the site look whatever you want. With mandatory ads things would be more difficult.