Parameters takes values, ignore takes keys. If you wanted to ignore positional args 1 and 3 using parameters it would have to have something along he lines of:

Parameters(args=(True, False, True))

Which seems less intuitive than

Ignore(args=[0,2])

And presents impossibilities when methods are defined in such cases as:

def foo(*args, **kwargs):
  # do stuff

Since it's impossible to specify the whole argument list...at best the Parameters style definition would be convoluted since it would consist of a partial args list.