Bottom line, it's an ego thing. Programming Languages of Choice Languages are very interesting things. They can either tie you up, or set you free. But no programming language can be everything to everyone, despite the fact that sometimes it looks like one does. It is quite interesting to me the amount of influence that programming languages have on the way programmers think about how they do things.
Syntactic abstraction is macros.
As opposed to other implementations of Scheme, Chez Scheme in my opinion has the best story on macros, and its macro system is among the most powerful I have seen. Control abstraction is the power to add new control operations to your language. For example, backtracking and coroutines. More esoterically, monads in direct-style code. I know I will be using Scheme for years to come, and my company will also continue to use it in its systems.