Strange. I seems like the soundtrack would only be released upon success of the movie or play, not the other way around. It's cool to write a concept album and be ambitious about it becoming a full-blown production, but the music also has to speak for itself. With KISS, their style was so firmly fixed already that a major departure from that could be fatal, as it apparently was. But Tommy was an album first, as was Quadrophenia, so what do I know?
Personally, I don't really think Music from The Elder sounds completely different from earlier stuff; just KISS trying something new, and I have no problem with that. I can understand if some fans did, though.
As usual, it seems that the suits are at least partly responsible for the failure of the album. You can't just fuck with the track order of a concept album, for one thing. Obviously there's an order that makes sense with respect to the story. This isn't just some batch of songs which can be rearranged randomly or in order to put the lead single first or whatever. Also, I don't remember seeing any promotion for this album, and certainly nothing to clarify that it was a concept album. I won't lower myself to use some cliché about KISS fans not being able to understand a concept album or be willing to indulge something other than a random batch of songs, but I'm sure that there was at least some of that factoring in.