Reddit is doing this because it works and has real impact on the bottom line, and effectively zero impact on user retention. As long as users continue to behave the way they do it would be fiscally irresponsible to shareholders for the company not to do it, same with Twitter.
If you don't like it the best thing you can do is to bounce and never use the product again. Users doing this en masse is the only thing that will get companies to do anything differently.
This is such a short sighted thinking, aggravating users because it makes some "user retention" metric look good.
You can either remain the central forum hub of the internet, or be replaced when the next big thing comes around. Just think how many major websites came and went during those last short 20 years.
If you don't like it the best thing you can do is to bounce and never use the product again. Users doing this en masse is the only thing that will get companies to do anything differently.