He's closing it down after the current crop of themes is done. It was a good idea, but too many people disliked the idea of an organized theme week, so would launch various NSFW type weeks during weeks that others had chosen. Of all of the theme weeks that have appeared, they showed up out of nowhere, got support from top users, and trounced themes that should have gotten a lot more interest.
Theme weeks will die out soon enough. In the past, users would just announce a week starting that day, and then wonder why nobody participated. This was why ghostofchurch put the stream out there. It was a good idea, but when the inmates run the asylum, disorder seems to be the rule of the day.
It would be nice if the Mods did control the theme weeks, but that isn't going to happen under imgflip's current owners.