Which big mass spammers are you thinking of? The only ones I can think of are political campaigns; scams obviously can’t be compliant at all. And even political campaigns are having to switch providers once or twice a year since they generate over 90% of spam reports and don’t actually bother with even opt-out compliance.

Any legitimate business that’s actually compliant will respect opt-outs and actually stop texting after a STOP, and I seriously doubt they would actually survive if they blasted away with unsolicited a2p texting these days.