It's possible 99% of PR/marketing firms don't have armies of Reddit/Twitter bot accounts, while at the same time the 1% that do make up a big power base on Reddit.
There are plenty of companies doing things like SEO and suchlike that build up networks of websites/content farms, and bots to comment on blogs and suchlike. Not much of a jump from bots commenting links on blogs to bots commenting more subtle messages on Reddit.
There is no 1% of PR firms that have Reddit/Twitter bot armies, that's a crazy conspiracy theory.
There are also plenty of companies that are "doing things like SEO" but none of them run networks of interconnected websites that they all control or content farms because those tactics stopped fooling Google over a decade ago.
There are plenty of companies doing things like SEO and suchlike that build up networks of websites/content farms, and bots to comment on blogs and suchlike. Not much of a jump from bots commenting links on blogs to bots commenting more subtle messages on Reddit.