The FCC has been cracking down on companies using long codes for SMS services because those long codes aren't required to follow the normal SMS rules concerning opting in, opting out, opt less keywords (help messages). For short codes the phone companies each test the short code to confirm it's following the rules.

Further, these long codes switch companies frequently as they get reused when they're no longer in use, and SMS user numbers have been spammed with sms messages as a result.