Tumblr style is a product of laziness and lack of observing the human form. A proper example of the human form stylized in an appealing way is Ayami Kojima, aka the Castlevania artist.
She follows the rule of eye/nose/mouth proportion while making facial features visually appealing and Gothic. Ayami is inspired by more classical art movements like Baroque and Rococo and she implements it well in a contemporary way. She simply observes the human face and avoids adding on features like bizarre mouths or oddly placed eyes to prevent pulling the viewer out of the art.
Tumblr artists are inspired by other tumblr artists. A domino effect takes place and the art gene pool mutates worse with each iteration. Simply put, tumblr artists suck because they lack formal understanding and practice of the fine arts. They are lazy and make art for the sake of making art, rather than pushing boundaries and learning from artists who made great art.
Speaking as a person dealing with art academia, most students are horrendously lazy and prefer to socialize/circlejerk each other rather than push their art to the limit. Ambition is scarce in the current climate of art, so we are forced to deal with shitty artists with bad attitudes who will never make provocative work.