Why doesn't Microsoft bundle third-party programs?

Yes, it has been done in the past, but the results were hardly a slam dunk success.

Who ports the software to 64-bit Windows? (Answer: Me, personally. I spent a good chunk of the year 2000 porting millions of lines of code to 64-bit Windows. Just for fun, I did a wc -l on a couple of the "gifts" that I ported. Over 100,000 lines of code in one of them, and over 50,000 in another.)

Who fixes the security holes in the software? (Answer: Me and people I work with.)

Who has to pay all the software taxes that the original software vendor failed to address? (Answer: Me and people I work with.)

Who has to update the program to keep up with new Windows design guidelines? (Answer: Me and people I work with.)

Who has to make the program localizable? (Answer: Microsoft.)

Who has to translate the software into 20+ languages? (Answer: Microsoft.)

Who gets sued if there is a patent violation in the software? (Answer: Microsoft.)

Will people realize that the bundled tools are included merely as a courtesy and that applications should not rely on their continued presence? (Answer: No.)

I know this from personal experience. When somebody gives you a gift of code, it's more often than not a burden in disguise.

And that's not counting the legal and public relations challenges some commenters in the linked article have raised. I mean, heck, Windows Vista simply included some photographs from the user community and look at all the anger that generated, both in the comments and elsewhere. And those were just photos!

(Some people might notice that this is the flip side of free code samples.)