Why can't parameter names start with a number?

Question

Variable names can be numeric-alpha, why can't parameter names behave this way as well?

Answer 1

Because the first-parameter-char of the command-parameter syntax as specified in the Powershell Language Specification does not allow for it.

2.3.4 Parameters
Syntax:

    command-parameter:
        dash   first-parameter-char   parameter-chars   colonopt

    first-parameter-char:
        A Unicode character of classes Lu, Ll, Lt, Lm, or Lo
        _   (The underscore character U+005F)
        ?

You can find a list of unicode character classes here.