First off the CAN SPAM act is flawed. It breaks stricter state laws and legitimizes unsolicited commercial email. Spamhaus calls it the YOU-CAN-SPAM act because it legalizes spam instead of banning it.
As for how the forces actually work, it’s a twofold. The first force is the market pressure of consumers demanding that solicited commercial email include more information about the opt-out so they know that they won’t be enabling spammers.
The second force is international trademark law for spammers who claim to be spamming on behalf of a recognized company like Amazon™. Amazon could pursue damages under trademark law, and in fact would have a legal obligation to do so. The USPTO will mark a trademark “dead” if unauthorized trademark usage isn’t challenged.
That would combine to let people opt-out of solicited commercial email while avoiding helping out the unsolicited. Spam is ultimately a social problem and the only solution is education and teaching people not to buy anything from spammers.