The issue is (in any scenario) the time it takes to do this (best is 8 months) and the expenditure and experimentation in between. Thankfully we know the methods which the Union could use thanks to the fact Joseph Leconte of South Carolina did some research on the matter for the Confederacy.
The issue is not manpower and resources, but the time it takes to produce the right chemical combination from scratch. It's expensive, time consuming, and labor intensive.
The CSA was a backwater, the US wasn't. Eight months is far from 2 years. This is something that was done for centuries. It isn't like Americans were idiots. The US was among the highest educated people in the World by that time. One thing the US is noted for is cranking up production when needed very quickly.