Simple. IBM filed first.
Reminds me of the "online shopping cart" patent that was sueing all major e-retailers years ago. https://arstechnica.com/tech-policy/2013/01/how-newegg-crush...
The difference here, is IBM loves to license out their innovations. And I think that makes it easier (cheaper) for Facebook, Google, Amazon, to decide to pay the fee rather than battle in court.