Simple answer: because he wants to. Antonio (Nysthi) has stated more than once that he makes his modules for himself. He is kind enough to release them publicly in case anyone else wants to use them too. They are free. It’s the biggest single collection in Rack. He has collaborated with Pyer on the design of some of his modules like Simpliciter and the 208 series - they are still quite tightly packed but the UI is improved.
Having said that, in the past, when people have pointed out that there isn’t a module in Rack that does X, a Nysthi module that does exactly that has usually appeared quickly, often within hours - which makes me a little suspicious that Antonio does sometimes make modules for other people too - not just himself 
. A couple of years back, when I mentioned there was no tuning and calibration offset module for hardware analog VCOs in Rack, Antonio immediately contacted me asking for a spec of what such a module needed to do and Tunathor appeared the same day (this was before the Silent Way collection made it to Rack). I’ll always be grateful for that.
Please don’t complain about free stuff. If you don’t like it, use something else. There are plenty of other envelopes. Or better yet, code your own and release it for free. If you don’t like small modules it’s probably worth avoiding anything with µ in the name…
I’m pretty sure Antonio has a hardware Eurorack btw…