Exactly the same reason you might write a program in C instead of in assembly language.
Well, NO!
Talking about my paid jobs, VHDL is *THE* language to design HDL stuff, and I have collected a lot of job-experiences for this, as well as professional tools for this.
Now RISCV appears and when you look at the code, a lot of projects come written in another HDL language for which I have to start from the beginning.
It's not like Assembly vs C, it's a matter of reasons and purpose. Now, or this new language has valid points, or I will avoid spending my time (and probably money) on it.