This is not a complaint but a question: Why?

Brompton is currenttly selling over 50.000 bikes a year and is aiming at the 100.000 mark by 2020, even though its bikes are a bit pricey for most people. So this is proof that there's demand for a compact folding bike for use in the city.

And since the patent expired quite a few years ago, why are the big boys still unable/unwilling to take the Brompton, improve it, build it in China, and offer it at around $€700-1,000?

At this point, we know of two Brompton knock-offs in carbon (Chedech, and Hummingbird), so they're even more expensive than the Brompton.