Or maybe suing for libel brings a lot of attention so unless it's very bad most companies will opt not to sue, especially if the target is a major news organization.
Er, Supermicro servers being surreptitiously implanted and installed in customer networks are existentially-threatening allegations against their business. I struggle to imagine what “very bad” would be in your view if that doesn’t rise to the bar.
More than the contents, the impact of the news on business is what would be used to decide. If most people think the news is likely fake there's no point giving extra attention to it by suing for libel. If it has enough impact to bring the company toward bankruptcy it will be an issue. Tbqh I wasn't even aware of that story until now.
I was reminded of this recently by a fursuit company issuing a C&D over an accusation most people had forgotten about, for a tweet that was almost half a year old at that point.
24 hours later, the tweet from the target of the C&D has over 7000 retweets and the response from the company has almost 1400 quote retweets yelling at them. Many of the angry responses have as many retweets as the company's tweet.
If that were true, those companies absolutely would have filed libel cases, because that sort of harm is exactly what libel suits are intended to redress.
Most likely, the story is true enough that the companies do not have a case for libel, even if specific details may be wrong, and the companies don't want a lawsuit because that opens then up to discovery proving that the foundational elements of the story are true.