Two words: They suck.
Forgive the harsh language, but I really find most crafts for preschool-age children not just gag-inducing, but developmentally questionable.
Whether it's making little bugs out of pipe cleaners and egg cartons, gluing cotton balls on Santa's beard, or adding decorations to a cut-out animal, preschool crafts always seem to be about nudging children to mimic or embellish something an adult has made.
Even in the most non-judgmental, non-pressured settings, such projects are more about competency -- the ability to place those cotton balls in just the right place -- than they are about creativity. They're often either so easy and unimaginative that they amount to dreary busy work for wee ones, or else require children to do things that are well above their skill level (meaning lots of "help" from adults).
Oh, and the projects are usually really lame.
Don't get me wrong: I love doing crafts. I made all kinds of wacky jewelry in my 20s, created elaborate scrapbooks in my 30s, and now enjoy unwinding in the evening by making altered clothes for my kids.
I just don't think there are many crafts that are appropriate for two-, three-, and four-year-old kids. (Readers, feel free to weigh in -- and, by all means, share any ideas you have for non-sucky, genuinely creative little-kid crafts.)
Kids in this age group are better off doing art instead of crafts: open-ended creation, in which there is no model to copy or modify, no right or wrong. They need lots of time and space to explore different materials and media, scribble and smear, combine and remix, generally mess around -- and use their own imagination to describe what they are creating.
There will be plenty of time, later, for cute creations, if your child is interested in such things. In early childhood, it strikes me as more important to nurture the sense of open-ended exploration that art provides.