1. People will not bother. It took a lot of minds to come up with the software used (in my friend's case, several PhD's amount of work). No one is going to invest that much effort to invent their own software libraries to get it to work.
2. Even when you do write your own version of the software, there are a lot of subtleties involved in, say, computational physics. Choices you make (inadvertently) affect the convergence and accuracy. My producing a software that gives different results could mean I had a bug. It could mean they did. It could mean we both did. Until both our codes are in the open, no one can know.
It is very unlikely that you'll have a case of one group's software giving one result and everyone else's giving another. More like everyone else giving different results.
Case in point:
https://physicstoday.scitation.org/do/10.1063/PT.6.1.2018082...
HN discussion: