Apparently enforcement is quietly coming down the pipeline. They're not doing enforcement out of nowhere because everyone knows that everyone is doing it, and it'd lead to the league enforcing against all teams simultaneously, which ultimately would be bad for the league itself to have at the very least none of it's star pitchers for some time period.
Enforcement is coming though apparently and you'll be able to see it in the stats pretty clearly in hindsight.
I don't agree with all MLB's descions, but at least in this case they're quietly optimizing for better games as best as they can given their massive bureaucracy which is what you want out of them.