Experimental licenses so far or straight up illegal, they're making much more money than any FCC fines would be. The FCC enforcement bureau is actually pretty small and doesn't come after you until you really screw up someone else's pre existing licensed service.
All FCC fines are public info (called a notice of apparent liability and published in their daily data dumps), I've yet to hear of one getting fined.
Do you have any sources/further reading? I'd be curious what type of licensing that operates under etc.
Edit: Turns out there's an article on it on the very same blog [2]!
[1] https://sniperinmahwah.wordpress.com/2014/09/22/hft-in-my-ba...
[2] https://sniperinmahwah.wordpress.com/2018/05/07/shortwave-tr...