I also agree that #6 is probably the biggest reason. Having to derivatize before injecting can be tedious, especially when you can dilute and shoot for many LC applicatiuons. I wrote a poster on analyzing cough and cold products by GC years ago, but our QC didn't like the idea.

I also agree that entrenchment is a big, but not impossible hurdle to overcome. If you could do an analysis that was fast, accurate, linear and precise, you could have the lion by the tail in our QC lab.