Because they can manufacture them easily, whereas normal human stem cells are hard to come by.
From which they can do various experimentation with regards human illness and genetic diseases.

Plus they are scientists and can do whatever the fuck they like. THEY HAVE LASERS!
(Jeru The Cunt of Monte Cristo, Tue 1 Apr 2008, 20:32, archived)

Your argument has convinced me wholly :)
LASERS! FTW?!?!
( Redsushi! Whoop Whoop! Like a Microfiche out of Waterstones...., Tue 1 Apr 2008, 20:45, archived)

"If I were creating the world I wouldn't mess about with butterflies and daffodils.
I would have started with lasers, eight o'clock, Day One!"
(Jeru The Cunt of Monte Cristo, Tue 1 Apr 2008, 20:50, archived)