I was also curious. It says this in about the middle of the homepage:

"We love LibreOffice. We are privileged to be the largest code contributors to the codebase, Collabora employs several founders of The Document Foundation, and many of the top committers. We offer a Long Term supported product based on LibreOffice, branded as Collabora Office Classic, and are deeply grateful for and acknowledge many skilled community contributors we work alongside, as well as the incredible range of features that LibreOffice code enables."