WOTC has all the numbers you have and yet they decided the OGL was not to their liking. I believe the reason is that it went too far. If the OGL didn't allow for other game systems and only allowed modules and campaign settings they'd have kept it. WOTC realized they needed new ip which is why they went the route they took
I'm not really sure that's it...
That's kind of the point of Open Source, which is what the OGL was based on. The idea being the users end up deciding which is "best" based on features, and not because it's just the only thing available.
For my part, I bought the core 3e books, and a couple other WoTC books, but most of my D&D money through the years was spent on 3pp books and products.
So, as I've said before, I think the OGL was great for consumers, and some companies, but maybe not so much for WoTC. (At least not directly.)
One could argue that it increased awareness of D&D, and therefore indirectly increased the player-base and potential customers... But who really knows?