One thing is to be said here: most people here really underestimate the casuals. As much as they're not deep into stuff as we are here, they're not oblivious to stuff that can be found on YouTube easily. I doubt it casuals aren't aware of GTH and SD.
Casuals
don't care about Got the Hots or Sunset Driver. They're the people who, if they pay 200 $ to see, say, Elton John, go to the bathroom or go get a beer the minute they hear unfamiliar notes, i.e. a song that's not on his greatest hits record. Assuming they even listen to disc 2, they'll turn it off once they realize it's demos with low-fi sound quality or songs that, while
we like them, are not Bille Jean-quality and thus will not hold casuals' interest.
As for people who are newer fans, that is people who are really getting into MJ's catalogue, they will get to Get the Hots and other deep tracks eventually, like we all did, once they've exhausted the main albums.
In both cases, it's entirely useless for those songs to be included on Thriller 40, as it's either un-needed for casuals who'll never even listen to disc 2, or un-needed for potential new fans who would have eventually gotten those tracks from TUC or the KOP discs, where they've already been released.
The only reason for disc 2 is money. The Estate wants you to buy an album you already have. So they have to add something new. But at the same time, because money, they don't want to put out ten new demos or outtakes, because they greedily want to keep those to get you to buy Thriller 50, and then Thriller 60.
It doesn't have to be this way. Other Estates are far more generous. And the MJ Estate will only join their ranks if projects like Thriller 40 fail.