Dev board prices are basically random. Disregarding these parts in particular, microcontrollers are a good option because they keep the process of actually bringing something to market simple and cheap, especially for a hobbyist. To go beyond an STM32 or similar (Kinetis, ATSAM, etc.) to an MPU, you end up having to use BGA parts which means board prototyping/manufacture is harder, you have lots of extra PCB design work and you'll probably be putting yocto or some other linux flavor on it which sounds nice but can be a pain. A microcontroller is one part, usually with exposed pins that are easy to hand solder, that you can stick on a PCB with a voltage regulator and maybe a crystal and have a fully functional design. You don't need to worry about board feature sizes/tolerances, high frequency/controlled impedance traces, and the mess of support circuitry that a basic MPU will require.
I know people like to write them off because it's so easy to get devboards with 1GHz+ MPUs and gigabytes of memory/flash on them but if you want to sell stuff, eventually you need to package the design and if you don't NEED linux, you can make your life so much easier and in most cases, have a much smaller product with way lower power consumption.
You don't pay for just the IC and PCB, you are also paying for the in my opinion, fantastic API and documentation that comes with the teensy. Plus, access to a platform that is fairly popular and its users seem to be more, well, advanced, than most arduino folks. Because of this, the forums tend to skew towards less noise and more technical matters.
They are expensive, yes, but I am comfortable buying a board from them every few years to use as my main chip.
I guess I am comparing them more to arduino / adafruit replacements, rather than more direct manufacturer prices. I have no experience with Nucleo boards but many other boards I tried out just hadn’t no community or body of libraries to draw from, whereas the teensy is pretty popular in the makers community. In my case I happened to need to drive 1,000’s of LEDs in real-time for an art piece and not only is there good software support, there is even dedicated hardware made for the teensy for this in the Octo Ws2812 board. I was so impressed with the quality and the size that I generally just use a teensy LC even when a $3 trinket would probably work. YMMV
I hear you. Check out the EPS32 [1][2]. It's faster, has more mem and has built in wifi, so you can access a webpage[3] on it via an ip and your browser and remote control it via your phone. FastLed runs on it, and there are level shifters similar to the Octo for it [4]. You can actually run 16 channels I believe (vs 8 on the Octo). It uses the same level shifter (x2) as the Octo. There is also an 8 channel available if you check the other products on Jason's store on that Tindie site[4]. It's arduino compat- so you probably wouldn't have to rewrite much at all.
There's an online IDE (which is similar in many ways to Arduino) with a whole ton of libraries, accessible from a, well, library, rather than having to hunt them down.
I know people like to write them off because it's so easy to get devboards with 1GHz+ MPUs and gigabytes of memory/flash on them but if you want to sell stuff, eventually you need to package the design and if you don't NEED linux, you can make your life so much easier and in most cases, have a much smaller product with way lower power consumption.