Well Reddit should just sue these companies and see if these companies are actually breaking any laws. Holding sizeable chunk of the internet hostage also sounds like something the EU and US might want to look in to as it very much sounds like anti-competitive conduct or market manipulation.
Also if these companies want to have greater ownership over the content generated by their users they should also be much more liable for the content posted to their sites. I mean when something like the Section 230 was written they probably did not take this in to account. If these companies want to start selling user generated content then they should simply lose the immunity from liability.