Why would a YC company use 99Designs for web design?

I'm a web designer and was talking to a YC company about designing their site. Instead of going with me or any designer for that matter, they put a contest up on 99designs with a whopping grand prize of $200. They kindly let me know that they would love for me to enter. Shouldn't a YC company know better? You would think the most sough-after mentos would tell their startups to invest in good design. Am i missing something here? Has any startup had a good experience designing their site with 99designs or similar sites?