In the concentrations necessary to make effective TATP? The acetone fumes are going to be noticable, although not necessarily tied to making explosives (I'll grant you that given the idiocy some people practice of doing their nails in-flight). But the peroxide is going to be pretty corrosive and sensitive at that concentration and would not conceal well; I'd be surprised if it wasn't picked up upon at some point. The stuff is also much more sensitive than nitroglycerine, so it's not exactly just "mix and chill" on the plane--if the guys mess up, they probably don't get enough made to do much damage, but they do blow their hands off and alert the crew.

And didn't DHS confirm that TATP was detectable by current ETD?

And this still doesn't address why NOW for the ban, and why not previously. The current ban clearly had about five minutes of thought put into it, and that just a brainstorming session (absent brains, mind you) to come up with a list of liquids people might normally carry onboard.