Because an elastic band does not involve a multi-million dollar contract. That's rather obvious.
Hi Rip,
Patent Details
Astronaut Mike Demonstrates the ARED Space Fitness Machine | NASA Science HD - YouTube
Departing Space Station Commander Provides Tour of Orbital Laboratory - YouTube
Do you think it's a good alternative to a barbell (given certain unique circumstances)?
Of course, a Russian wit in the Youtube comments asks "why don't you just use an elastic band?"
Because an elastic band does not involve a multi-million dollar contract. That's rather obvious.