The rule of thumb I've heard from accounting weenies in Hollyweird is that you take the total cost of the movie and multiply it by two--that is the box office take it must generate worldwide to make a profit, and that considers everything other revenue stream in the mix (since those streams tend to reflect a set percentage of the gross). The "movie reprint" of the book does not generate revenue for Hollyweird. The soundtrack revenue is small potatoes unless it generates some big hits.
The movie just wasn't very good--Hanks and Howard (who worked very well together on Apollo 13, so they can make a great movie when they're both passionate about it) just didn't seem to care, and it showed. They relied on the hype, instead of their own talent.
According to IMDB Sony "only" paid $6 million for the film rights (hard to classify $6 million as only).
The accounting weenies I've talked to is just compare the production budget to domestic gross, because domestic gross is such a small percentage of total gross the fact that they don't actually get all of it (movie theaters gotta make some money) is overpowered by all the other sources of revenue. So if domestic gross is at least production budget then the other 67 to 75% of the revenue will garauntee profitability.
Movie reprints include stills (at least one on the cover, sometimes more inside) from the movie and Hollywood makes darn sure they get paid. Now reprints don't generate as much revenue as novelizations, but they still make some money. Soundtrack might be chump change, but add enough piles of chump change and you got money ("a million here, a million there, pretty soon you're talking about real money"). The big sources of additional revenue for DVC will be foreign (already twice domestic), and DVD, with a couple of nice paychecks from HBO and some network (I'm guessing ABC) in there.
Doesn't matter if wasn't very good, the question is will it make money. Alf was one of the stupidest shows in the history of TV and still managed to run for 4 seasons. Movies that suck in pretty much every possible way of grading a movie have turned vast quantities of cash.