One of the aims and aspirations of the Open RAN alliance is to ensure that the technology is in fact open, a series of standards that aren't inherently captured by one organization or one company or another.
They are self-interested in getting involved in that because, right now, if you purchase equipment from any of the large vendors, it's quite expensive, and Open RAN currently promises to reduce those costs, so there is an incentive, even if they don't own the IP, to be involved in developing the standard itself.