Serious question: what are people building with these boards? The recurring projects I've seen are controlling lights, doors/locks and monitoring water in plants. I don't find these particularly compelling, am I missing something? How is this the next big thing?
The Arduino IDE and all the ecosystem of libraries and community could be the actual "big thing", because the Arduino is just a convenient development board; but you can get those from the chip manufacturers themselves (OK, may be now those are nicer because the Arduino boards).
I think the IDE is making the hobbyists able to work with microcontrollers in a very easy way; compared with all the tooling and docs you have to read to build your own dev board and program the MCU yourself.