You're confusing two things.

There is the "I see no nuns therefore there are no nuns" problem.

Then there is the shortage project...of why so few women are saying Yes to the religious life. 

One is exocentric, one is egocentric to the person. 

God doesn't need religious brothers and sisters any more when the US Gov't ensures hospital care for all, food banks, soup kitchens, and lay teachers.

Sisters have been "supplanted" by these other people and providers.  

It's like who needs unions for work place safety while there is OSHA at the US, state and country levels!!!   Another supplanting.