May be, contrary to fans' anticipation, Sony has no intention to make the album a blockbuster. May be Sony doesn't want to take risk. Sony may not want to invest more money in the overheads. Knowing how strong the brand Michael Jackson is globally, Sony knows Michael's core fan base would turn up and support the album; hence, the album will make a profit with minimal promotional budget.
Based on the worldwide performance of the album thus far, Sony is doing okay. Keep in mind, the production cost of this album is relatively low. The demos are all recorded and the songs are stored in the vault. No hours and hours of recording sessions were needed. Which other artist can give Sony a better chance of profitability? Very few. Sony doesn't need to spend money on promoting Michael Jackson for Michael Jackson is alreay such a well known brand. Sony doesn't need to incur high production cost neither.
Michael Jackson is like a blue-chip stock. Low risk and good value.
Then, why Sony would pay $250 million for the deal if it doesn't want to make huge profit? I guess it's mostly for Michael's iconic back catalog. Songs like Billie Jean are much more valuable than Hollywood Tonight. Of course, fans want unreleased materials because we own everything Michael released and we want something we have never heard of before. But, to the general audience, unreleased materials mean outtakes, incomplete songs. They may perceive outtakes as songs that are not good enough to make the album; hence, interest level is not as high.
Just my two cents...