There are many reasons, but mine is that that is not what I signed up for. The goal of my research is not to make a huge pile of money. It is to advance human knowledge. So when I discover something, I give it away. That's the goal. This is how universities are traditionally set up. With a few high-profile exceptions, it's largely how they are still set up.
This means I am unlikely to get rich. OTOH, I don't have to limit my ideas to those likely to make money, which is hugely freeing. I get to work on nifty stuff for decades without ever worrying about being even "Ramen profitable".
If I were in the position of Mark Bolas, I'd certainly be wistful about the billion dollars I might have had. I would probably be very unhappy that some work that built on mine did not even mention me. (In academia, we always give credit to those whose work we build on. It's an unbreakable rule.[1])
However, I would not be indignant or -- except for the lack of credit -- feel mistreated or owed anything. As I said, that is not what I signed up for.
[1] I personally get very annoyed when, as often happens, companies break this rule. I used to get into arguments about this with people at booths at conferences. I've mellowed a bit since then, I think, but it still annoys me.
At least in my field, in order to remain both functional and employed, we have to work on ideas that attract funding. For us to make effective use of our skills, there's a small but meaningful burn rate in hardware and machining costs.
An aside: It's totally possible for Oculus to make a substantial thank-you gift to Bolas.
Many commercially-plausible ideas coming from research labs are in fact patented and owned by the university. Companies which use these ideas are required to pay licensing fees or to purchase the patent. (Most research universities have a "technology transfer" office for this purpose, which famously are said to either lose money or make all their profit from only one or two patents.)
As a grad student, I was required to sign documents stating (in effect) that discoveries made by use of the university's resources were owned by the university.
That doesn't work very well at all for undergraduates, where they are formally paying the bill, vs. those who are being paid like hard subject graduate students, post-docs, faculty and staff.
E.g. MIT undergraduate theses are owned by the student.
