Why is Homo sapiens not categorized as an invasive species?
Ignoring for the moment the question of politics, let's consider the various definitions of the term "invasive species" that are in use. Colautti and MacIsaac write in their discussion of invasive species terminology (1):


  The greatest confusion [among the discussed ecological terms]
  surrounds the common term ‘invasive’ and its various derivatives
  (Richardson et al., 2000a). Explicit or implicit definitions for
  ‘invasive’ include: (1) a synonym for ‘nonindigenous’ (e.g. Goodwin et
  al., 1999; Radford &amp;Cousens, 2000); (2) an adjective for native or
  nonindigenous species (NIS) that have colonized natural areas (e.g.
  Burke &amp; Grime, 1996); (3) discrimination of NIS established in
  cultivated habitats (as ‘noninvasive’) from those established in
  natural habitats (e.g. Reichard &amp; Hamilton, 1997); (4) NIS that are
  widespread (e.g. van Clef &amp; Stiles, 2001); or (5) widespread NIS that
  have adverse effects on the invaded habitat (e.g. Davis &amp; Thompson,
  2000; Mack et al., 2000).


Note that except for #2, all the definitions require that the species is a nonindigenous (non-native) species in the area under consideration. Therefore, while humans may be considered to have been an invasive species for much of our species history, under most definitions of the term we no longer qualify because except in a few places (mainly the arctic, antarctic and marine environments, where human presence is minimal) we are now a native species.

See also http://www.smithsonianmag.com/science-nature/are-humans-an-invasive-species-42999965/?no-ist