Gwen Tennyson has been portrayed at basically every major age bracket of her life. her original 10 year old look and outfit is by far the most iconic. When it comes to aged up fanart of a lewd or cheesecakey variety many artists tend to just make their own design more closely based on the original art style version of Gwen instead of Adult Gwendolyn from the Ben 10K episodes or Teen Gwen the UAF/Omniverse Eras. Besides aesthetic preferences I chalk it up to ignorance as many people are just secondaries that just draw Gwen because she's popular and well known instead of any actual series knowledge, with extreme lore/dialogue fumbles like thinking she's Ben's sister or Grandpa Max's niece or fooling themselves into thinking she's some kind of bratty little tomboy minx when she's actually a goody two shoes preppy know-it-all. Either way all forms of Gwen need love.
Except UAF Flashback/AF Picture Gwen we don't talk about that one