You are leaving out the tinkerers. Building and adjusting an exhaust system can and will lead to making deposits when exhaust gas flow isn't optimal. In cases where there is no way to get perfect tuning length it will be an ongoing process of carbon build up. Finding the perfect tune length to a exhaust system being the goal. But before finding the goal I've had to disassemble an engine every few weeks to unstick rings and check for deposits.
During this time I will use Seafoam to;
Keep the carbon soft so it's easy to remove,
Help clean a dirty engine after finding tune,
Use in engines where I need/want to run a larger prop. Nothing will stop this engine scenario from building enough heat to make deposits. The Seafoam keeps it soft. Adding some dino oil to the mix seams to help also.
Running standard mufflers though, probably would not lead to needing to use Seafoam. None of my engines have standard in cowel mufflers. (except maybe running too large of a prop) So I can't say much about them.