To convince you, I can say that apps need SMTs if the current Hive token does not solve their problem. Though might ne some apps need to control everything like their power down, inflation and for them SMTs is the good fit.

SMTs are needed by companies that want to build rewarding systems of their own for their websites like Reddit has done with an ERC-20 token. Hive is completely superior to Ethereum when it comes to facilitating a large number of small transactions. That's how you could onboard users in much larger chunks than by trying to get them to use Hive front ends one by one.

Your imagination is very limited. SMTs can be used for way more things than the uselessness we've seen with HIVE engine. 

Creating a coin with an inflation and designing the right sinks to burn it, in a game for example, will provide great usecases. Or even just use inflation and back the token with half of the app revenue. 

It allows developers to ICO their own token for their own platform and for their own specific purpose, tweaked with inflation rates and special sinks. 

Not everyone wants to integrate HIVE. HIVE is the RC token.