It's like a rocket. Most of the fuel in a rocket goes towards lifting the rest of the fuel. Likewise, Twitter needs that level of investment to scale to the point where it can make a return on that level of investment.
This is a good analogy. But with 800m raised in 2011, arguably when they were close "escape velocity" already, its also a fair point to wonder if destiny could have been any different with less $$$ weighing them down.