The reason it's like this (and I agree it sucks) is that this kind of software is quite complex to develop and the likely userbase is very small. If you're a hobbyist or even a professional engineer and your goal is to make a specific thing to accomplish a task, rather than use a specific technology, well over 99% of the projects you can think of doing will be much better served by a commodity microprocessor than an FPGA. And cheap MCUs are getting faster every day, so certain things that might have needed an FPGA in the past can make do with programmable microcontroller I/O and maybe an affordable DSP chip today.