Some companies find that while they have no problems going open, they are using proprietary components by other copmpanies which object to that. Don't lock yourself in.
And why should they? They should go libre.
Because they're greedy.
Because the CEOs like their planes.
Maybe they could but they don't seem to have enough imagination to come up with a business model that would make that possible. I've also heard that their code is very messy and that would be embarassing.