Reddit grew to the point where its audience is now a lot more broad and the previous audience is a vocal minority. They can get away with ramping up ads and other behaviour because the audience is no longer sufficiently monolithic to revolt.
Bearing in mind in the past the audience did revolt and basically kicked out the then CEO (temporary CEO but still...) Ellen Pao, in what was a kind of full scale riot that shut most of the site.
Remember that YC is an investment company. They certainly made billions of dollars through the companies they funded, that were in part thanks to HN.
Every time you send a direct job application to a HN company, that's 20% of your yearly salary staying in the company instead of going to recruiter fees. That's the hell of a revenue per click.
While admire that CN is not squeezing them to death, it appears like Reddit is vastly under-managed.