It should be more common, but I suspect it is not because it makes parsing languages more complex.
Benefits:
- Upholds the principle of least surprise
- Reads like math is taught
- Reduces cognitive load (see previous 2 points)
Drawbacks:
- Grammar is more complex for the language
- Special case syntactic sugar
As to why not, my guesses are:
- Language author(s) didn’t think of it
- Is on the ‘nice to have’ list
- Was decided that it wasn’t useful enough to justify implementing