Here is the reason, it isn't Nascar but the team owners, money also it looks like
WHY NO CHANGES TO THE PACKAGE FOR SHORT TRACKS, ROAD COURSES?
Even if not everyone agrees on the changes to the racing product for intermediate tracks, everyone seems to agree that the high downforce has had a significant negative effect on short tracks and road courses.
The reason NASCAR didn’t order a reduction in downforce for short tracks and road courses for 2020 is the same reason why it didn’t for 2019: team owners.
The team owners did not want to develop two aero packages simultaneously,
in addition to two different engine packages.
https://autoweek.com/article/monste...wnforce-makes-big-cost-containment-swing-2020