Photographers don't just "go after" big companies though. They go after whoever is infringing on their copyright. It is the individual users who are infringing on copyright when they use copyright images. If a big company is infringing, then of course they will assert their rights with them. But they don't "go after" websites. They just send DMCA takedown notices to make websites comply. The website (like Steemit) must then inform a user that they have removed the copyright material. If a user offends repeatedly, they are supposed to be removed from the website.

Most service providers and websites have what is known as "safe havens." That means that as long as they educate users about copyright, take down infringed material, remove repeat offenders, etc., they have limited liability. I'm not sure how Steemit stands in that. I think Steemit (and that means ALL OF US) would be in huge trouble, because there is no education about copyright listed anywhere and no intolerance to copyright infringement, plus, there is no material anywhere telling a creator how to file a DMCA notice. All that is required in order to make a website in compliance. Under whois Steemit is listed as being registered in NY, so it is centralized enough under that information!