They don't allow companies like Perler to signup. What Perler used AWS for is prohibited by the TOS and AUP that Perler agreed to. It just took a while for AWS to notice and enforce the legal agreement that Perler agreed to abide by. Perler lied right from the beginning (because they had no intention of abiding by their agreement) to get AWS to provide service they would never have provided had Perler been honest from the start.
Also the cake issue is different because discriminating based on sexual orientation was prohibited by the Colorado Anti-Discrimination Act. Colorado (the state I live in) has every right to pass laws to govern it's citizens. What happened to state's rights?
To me these are very clear: You either believe contracts and laws can be enforced, or you don't.