Snakes, CGI's last conquest?

So I was watching Stephen King's Nightmares and Dreamscapes the other night. There was a story about a guy who was bitten by a snake and was paralysed. The whole story took place around doctors thinking he was dead and getting ready to perform an autopsy while the guy was aware of everything going on but could do nothing. A very frightening idea indeed, but when they showed the snake it was very obvious it was computer animated. I kind of brushed off its crudness to it being just a mini series on television, but then I remembered the trailer for Snakes on a Plane where the snakes looked just as bad (if not worse in some shots). I went on to realize that just about every snake I've seen (in movies, commercials, television) since CGI became prevelant in movies looked like garbage. They all look like they're made of plastic and have a certain glimmer to them that you wouldnt see on live snakes. Also I think the actual animation of the snake can never be as smooth as the snakes movement itself (or maybe the animation is too smooth). They always seem to stand out in any scene they are in . So why is this? Why after about 12 or 13 years of CGI in movies everything else looks nearly flawless while all snakes look like they were modeled, rendered and animated in 1993?

I am not a computer animator so I call out to you that are, to answer this question. Why do all 3d snakes suck no matter the budget and no matter the year? Maybe the trailer for "Snakes on a Plane" was rushed out and the effects weren't complete. Maybe it will come out to rave reviews of how realistic and scary the snakes look and all my confusions will be put to rest by Sam Jackson and his crew.