Because if things go some people are predicting here, .uk is going to be the main choice for a UK website. Clearly they would then want their .uk to avoid losing any type ins.
If you wanted to visit the Natural History Museum, and you knew .uk was the main extension for the country you were looking at, would naturalhistorymuseum.uk not be a good place to start looking? I know they're actually on NHM rather than the full words... but you know what I mean.
So isn't it better for non profit organisations to stay on org.uk to avoid confusion.
If I am looking for gosh.org.uk I know where to go.