Because you have to write multiple-value-bind yourself, no &optional and &key parameters, no try/catch or condition system and verious other reasons. Scheme is

Because you have to write multiple-value-bind yourself, no &optional and &key parameters, no try/catch or condition system and verious other reasons. Scheme is case sensitive by default though, which I like. It's sort of like asking 'Why C++ and not C?'. It's the features or lack thereof that you have to want or not want that lead you to your initial decision. Then you switch to the other to see what you're missing. Then you make up your mind.