It may be interesting to note that Joe Kaminkow mentioned recently (I think on the Head2Head pinball podcast) that (assuming he was referring to Beatles) he gave this license a new shot and had Christopher Franchi do some artwork to show the licensor. Apparently, that's what got them interested in licensing the theme to Ka-Pow/Stern. So, while many may not like the shown artwork, the licensor must have thought it was great. From that point on, Stern's hands may have been tight due to licensor's approval. This is all pure speculation, but don't underestimate the power of a licensor.
In addition: if the $50k price tag for the Diamond Edition is correct (and so far most of what has been rumored has been correct) then only selling these 100 games brings in $5,000,000. The license was apparently $1.000.000, so they still have a $4M turnover by making 100 games. Even if they don't make the other models that's a huge profit for Stern. If they do sell the other games, more profit for them.