That, and the simple fact that there's no reason to leave EASA. EASA grew out of JAA, but JAA was far bigger than just the EU, and so unsurprisingly is EASA. It has 12 full members who aren't EU members, and as Britain has the world's second largest aerospace industry, not to mention massive supply chains into various other corners of the EASA regulated world.
Basically there's no reason to leave EASA, and some very good reasons not to.
To most of these, of-course, we in light GA are pretty much an irrelevance. All decisions will be driven by the high value heavy metal.
G