IBM had their own Basic, 4 of them really (collectively called IBM Basic) that was a barrier for the clones[1] (eg, Compaq, Dell, etc) because they wouldn't license it. (You probably used one of them, basica if you used the classic PC)

Microsoft made GW basic and smited IBM by putting it on the clones Except for the IBM machines. They also intentionally made it slightly incompatible with IBM's basic. Then they held the GW basic source hostage so IBM couldn't resolve the inconsistencies, couldn't backwards engineer it because of the licensing, and thus put them at a losing negotiating position since Microsoft now called the shots because they controlled the software. (I wonder if this slight is in the comments, let me go look, that'd be great[2])

Microsoft also held the DOS source code hostage and it was a huge stickling point in the OS/2 and Windows work and was a significant reason Microsoft was able to steal the show from IBM. IBM even sent over a bunch of engineers to get DOS 2 to work because DOS 1.1 was a complete mess. But they didn't have the rights to walk out the building with the source they wrote due to a contract oversight.

Bill Gates was a true software Napoleon, it's really quite something.

Now they're releasing all of it. It's a strange coincidence to pick the three they burned IBM with 35 years ago...

Maybe they're trying to shake off the old days, maybe they're putting a final stick in IBMs eye, maybe it's genuinely unrelated, who knows.

Smacking around IBM is my preferred reading because the idea of doing one final power play, against IBM for God sakes, 25 years after it became unarguably 100% meaningless with the release of Windows 95, I personally find hilarious.

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[1] The only source code left in the timeline we don't have is Phoenix, who cleanroom cloned IBM's BIOS in 1983 (using a Chinese Wall) which allowed the clones to really take off. But they've been pieced off and sold as a fleamarket to HPE, Absolute, and Marlin, so who knows when we'll see that source.

[2] I'm going to make the bold claim (after 10 minutes of poking) and say either they removed the incriminating things or the claimed intentionality of the incompatibility is now provably just a rumor (as in they lucked into it through implementing an imperfect clone)

There's evidence for both I guess. For instance, GIOCOM.ASM has a reference:

COMPAQ=0 ;Include IBM 1.0/1.1 Bugs for compatibility

But this isn't cited anywhere else. It's just hanging. They have a bunch of other vendor specific things like ZENITH, TSHIBA, they all have logic, this one is absent any logic, it's just an orphan. Shrug...

I just tweeted @ BillG and asked him --- snowballs' chance he'll respond but who knows.