That explains it

Kent Pitman:

I certainly sat in lots of Scheme design meetings where I pushed for obvious things like branch cuts, error handling, and other "useful" things and was told that such things would ... make the language "too useful" [thus meaning too many people would flock to it and it would be the end of the designers' ability to do the things to the language that _they_ wanted to do].

Seriously though, this shows that the forces behind Scheme are far from obvious.