Going back to history, TSA PreCheck was not really designed for general public.
It was designed for the purpose of expediting travelers who were deemed low risk, like frequent flyer. Hence, enrollment was not available at that time.
Now - TSA sees this as a cash cow. Hence, encouraging everyone to get it or sponsor it.
FWIW - when the writer of the article has to pay for TSA PreCheck, he really does not know a thing or 2 about TSA PreCheck.
(Note - I have never paid directly for TSA PreCheck.)