There's something dishonest and cruel about wrapping presents. It represents hierarchy and process, which seems to impede the receiver and add tantalization for the giver; this is all well and good if we're talking about a relationship built on power dynamics or some S&M thrills, but it complicates things with friends and those whom you love.
This is especially the case with children. Wrapped gifts are a useful device for keeping the youth in line. They're like brightly-wrapped time-delay explosive devices that turn children into agents of espionage.
Another reason why I don't wrap gifts is because I am terrible at it. Some people have a gift for aesthetics and design and they use it in the presentation of gifts and it's gorgeous and amazing, and I just feel like an oaf in the process.
There are people who derive a great deal of joy from wrapping gifts. There are people who earn a decent seasonal income from doing it. But not me.
So there you go.