You're right that they're being thrown together way too quickly to cash in on the success of Mamma Mia. That's always the case with something so popular that's viewed as easy to pull off.
But here's your first-level list of steps for any would-be writers out there...
JUKEBOX 101...
1) Find a song catalogue with a lot of up-tempo material and a FEW well-chosen ballads. (A FEW only.) The up-tempo songs could be anything: dramatic, happy, scary, etc. but they will drive the pace of your show and define its energy.
2) Make sure nearly all of the songs have an emotional through-line, and they don't just hammer a repetetive "hook" without any advancement of thought or feeling. (You can throw them a catchy bit of fluff every now and then for its sheer fun aspect, and it will work... but it can't be all like that or you won't have any weight to the show.)
3) (the obvious)... Be creative! For a "jukebox" musical... it's ALL about the book and the solid intigration of the songs. That will make it seem new. Otherwise, they'll be sorry they didn't just go out and buy a best-of CD.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22