That’s not a lot of companies when you consider the thousands of TTRPG out there. The question wasn’t: is it in their best interests?
The question was: is a company obliged to release an SRD of their rules else be branded a pariah?
The protected characteristic around TTRPG rules has never been tested in court and is just one of those claims bandied around the interest without any substantial evidence. Even if rules aren’t protected are companies expected to make it easier for outsiders to copy their work? Irrespective of these points, while rolling 1d20 and adding a number may not be protected, there is still plenty of creative expression around rules content that would be - the 200+ spells for instance, or the feats or the unique magic items. Or the unique creatures.
What about the publishers that don’t do it? Cubicle 7 for instance with the doctor who games, or Warhammer license? What about board games? Are the makers of Eldritch Horror expected to release their rules for free on the internet? What about other games?