Why can't main class be given in module-info.java?

[Gunnar Morling]

Hi,

Why is it that the binary form of module declarations can carry
information on a main class ("ModuleMainClass" attribute), but no main
class can be specified in module-info.java?

It seems setting ModuleMainClass is left to the jar tool, but I'd like
to understand the rationale behind it.

Thanks,

--Gunnar