Why are anime characters usually drawn without lips? I have noticed that most anime characters are drawn without lips. Is there a specific reason for doing this?
The reason seems to be more historical and technological than some kind of art or costumes. Realistic lips are hard to draw. The lips has certain singularities that prevent creatives from trying to imitate them. In cases where they need a close up (focus on) the lips, the quality/relistic could be increased (this depends greatly on the production) but in most of case whereas there is another more important elements in the scene, some realistic details are just dropped.

Of course, some technology could allow producers to pimp up all realistic features (lips included) so they picture more realistic lips.

In a single line, the answers is: if they are not pictured, is because it results a pain to produce them; if they are pictured is because all other details are also realistic, why not lips.