Publicly traded companies are actually under a legal compulsion to always make the most profitable decision. If they don't, their shareholders can sue them and easily win and bankrupt the company. It's a dirty open secret about publicly traded companies and the legal system. Once you go IPO, you lose control of the company, because you have this constant legal threat that limits your decision-making abilities.

This will almost guarantee reddit will redesign itself to suit advertisers to generate the most income (because literally by law it has to), which makes it very likely reddit will go the way of digg.com, given enough time.