Assuming that the only problem is that they are inexperienced...
On a team of that size, you're not only doing development, you are (or should be) grooming future senior devs. In the enterprise world, on timelines that run 5-10 years, with groups 100+ in number, you have an entire ecosystem to manage.
Also, in groups of that size, you're going to make mistakes in hiring. I've seen the same thing on small teams, where the whole team interviews someone who ends up sucking. With a 95% success rate, with 100 people, you're still talking five screwups.
Breaking things into smaller teams doesn't necessarily get you what you want, either. You end up with a bunch more management, turf wars, and a bunch of other hard-to-deal with crap.
Basically, at the really large scale, it is less about the code, and a lot more about managing people over a long timeline.