The intelligent ghouls are estimated to be about or over 200 years old.
The ferals are the ghouls who have 'spoiled', ie, suffered brain rot to the point of losing all intelligence.
Now lets take a US population in the 50's, say 1959 so 177,829,628 people.
Lets kill 50 percent of them in Atomic fireballs leaving us 88,914,814 survivors.
Lets say 10% of them survive the radiation thanks to science and chemistry: 8,891,481
Lets say 10% of them survive the next 200 years as ghouls: 889,148
Now 10% of them go feral: 88,914
If we divided this number by 50 states we end up with 1778 ferals per state.
Now exactly how many Ferals have you counted in Point Lookout and DC Wasteland?
Less than their statistical probability I bet.
Also note that during the past 200 years people are born, like the lone wander, Moira, James, Dr. Li, etc.
These people after radiation exposure, and exposure to such fine drugs as Radaway, also
turn into your average wastelander/pitt person and go ghoul (or trog) eventually.
These ghoulified people will go feral one day, brain damaged persons like drug addled raiders probably sooner than others.