Well, the thing that stops you is the cost of designing, implementing, maintaining, and scaling the replica testbed. On a large network, that would be pretty hard to justify to most organizations, which would see it as very costly with a tough-to-measure upside.
Have you done this before? I'd be interested to hear how those conversations went.
For an organization like CF? Yes, I would expect them to have testing and network simulations down to an art.
If I had to guess, I'd say it's because network engineers simply don't need / get this know-how on normal scale. Most SW developers on the other hand are not very good (good enough for CF scale) at networking. Which leads to networking guys doing their thing the way it was always done... (hope I didn't offend anyone, just guessing)
I hope they strengthen their dev department... I know I'd love a challenge like that. :)
Have you done this before? I'd be interested to hear how those conversations went.