Why the switch? Maintaining a Wordpress site is annoying in the long term. Upgrades are needed on a regular basis for security patches, which is to be expected from a fairly large web application. However having to deal with styling issues from using a custom theme, and dealing with plugin incompatibilites every time isn't something I want to deal with for a simple site.
Pelican includes the features I want (themes, code highlighting, etc) without the hassle of dealing with a site which I need to upgrade every few months.