Quoted from Manbearpig:
Stern was on a roll when they put out IM, Tron, AC/DC, Metallica, and Star Trek. Basically music and Scif games are what sell. I feel like more listening to the pinball community would help drive future sales. Putting out games like Mustang and WWE are not as popular with everyone so the theme kills it regardless of toys and gameplay.
I understand why they're trying games like WWE and Mustang...they're not trying to appeal to "us" - the pinheads - they're trying to show new groups of people that pinball exists, and in that sense, those games might be "successful enough". Lets just say these games aren't hits but at least break even...the media exposure (Mustang at Ford shows, for example) makes it worth it. Since Stern always has many games on the production line, games like these not being hits doesn't destroy them...they're still selling Walking Dead, Star Trek, Metallica, etc.