The single fold in the middle is old technology, and would be well beyond any patents.

I wouldn't be surprised if some of the bikes showing up are made by the same factory with different logos. Nonetheless, the required engineering would be minimal.

The single fold in the middle is also quick and easy to do. What is the additional space savings of bikes that fold around the bottom bracket, and incorporate several folds?

One of the limitations of folding bicycles is dealing with the chain and driveline. One can't simply fold the chain. So, either one rotates the rear triangle around the bottom bracket, or folds the bike in front of the bottom bracket.

One can't shorten the chain stays too much. I bought a cheap Citta folding bike, and have a lot of troubles keeping the front wheel on the ground when riding up my driveway due to awkward weight distribution. I have to do some rebuilding before the bike is truly usable.

Consumers obviously like lots of options and cheap bikes, but I'm glad that some of the bikes like Bike Friday, Birdy, or Brompton can buck the trends and make quality unique bikes. Bike Friday is still manufactured here in the USA.