Here's the problem:
- All those soldiers need a place to stay. So do their family members.
- They need equipment that doesn't exist right now - weapons, radios, vehicles, etc
- The equipment needs people to maintain them
- The maintainers need a place to maintain the equipment
- Those soldiers have to be trained; the increased load on training posts will require more trainers, more equipment, and facilities
New units' needs are very expensive. I think that was one of the reasons that the Army started looking at brigades vs divisions. There's not all the "overhead" that a division headquarters brings. And that overhead can be put into support for the brigades.
When they cut the Army the last time, that was probably the last time we'll see an Army of that size. You can see the dominoes that have to fall to expand.
Bottom line is always: $$$$$