Hobbyist is not a skill level designation. It means someone is doing a particular activity for fun, typically not associated with a business.
There are hobbyist who wire up an LED, make it blink and get immense satisfaction out of that. There are also hobbyist who putter around with a scanning electron microscope in their shed, and everything in between.
There are hobbyist who learn the things you mention and more.
> Programming in HDL is fundamentally different from C++ or Python..
Ok? And cheese making is fundamentally different from radio astronomy. Yet there are hobbyist pursuing both.
> I just don't get the allure of fpgas from amateurs who don't need to use them for work.
Let me give you an example. One summer when i was younger I have found a Xilinx Spartan dev board in a dusty bin in our hackspace. Nobody around me did know anything about it, it was probably a donation originally. I spent about two weeks playing with that thing. The most advanced stuff I ever got working was some example code found on the internet which synthetised a pong game through a vga connector. It was generating the video signal through just turning its outputs on and off in the right patterns. That was total magic to me. I spent the time understanding every line of the code and modifying it to do different things. I was goofing off, learning about tech, and having a great time.
I’m not saying this is the only way to enjoy an FPGA, but it certainly illustrates that hobbyist can get value out of one.