Give me one good reason why that musical had to become a movie.
To make Money, money, money!
I mean the original musical was very popular and had already been seen by millions of people around to globe so Hollywood being Hollywood decided that they should make a movie out of it to cash in on it's success...
Those people who actually watched it (35+ years old) will remember watching it, but what do they remember about the show itself?
We soapfans are not the majority.
No but I am just saying that Dallas is a famous show. It was on a channel that most people had access to at a time where cable TV was still unusual. So in some countries you only had two options, which means that pretty much half of the population of those countries watched Dallas. Even now most people have heard of it, in parts due to the revival which gave it a new younger audience.
The show they replaced it with I had to google to even know what it is. It's on Netflix, meaning a large chunk of the population doesn't even have access to watch it.
Also since "Mamma Mia" is a "Sing-a-long party" why change the original lyrics of the song?
Because if people go to the cinema and doesn't know of the change they are bound to end up singing "the wrong" lyrics!
