Why call is not calling like native primitives? even when var is otherwise undef?

[Garreau\, Alexandre]

Why not, like in shell, when some function/variable is undefined, call
an internal one when defined? What’s the historic reason of this?

For instance, if there’s an occurence of $(several words) in the
makefile, and the variable “several words” isn’t defined (that’s not a
natural thing to do anyway), taking its firstword, and being equivalent
to $(call several,words) might improve readability, be simpler,
etc. then why not?

And then I asked myself, if some functions weren’t deemed useful enough
to get integrated as native primitives implemented in C, why do we still
need to use the $(call fun,args) syntax when it could be done like shell
and decide that any multi-word undefined reference could take its
firstword and use it as call does? like if in “$(fun args)”, the
variable “fun args” being if not undefinable, at least inaccessible, if
the "fun" variable exists, make it equivalent to “$(call fun,args)”?

Thank you for your time, hoping my message isn’t too much confuse or
disrelevant…