The version of declarative in the OP is one which I would describe as “factoring out functions plus a fancy DSL”. There are times where you want a fancy DSL, usually for aesthetic reasons. Like, it’s kinda nice that Ecto queries look like SQL so they’re recognizable. And as for factoring, we all know how to do that.
As far as I can tell we have entire frameworks built around that declarative (e.g. Ash) and TBH I don’t really get it either, but hopefully someone else can provide the defense you’re looking for.
However, I think you understand “my” declarative more than you realize:
What is letting it crash but rebuilding the program from scratch? 
This is actually exactly the same concept. OTP supervision and React components take the same fundamental idea of “turn it off and on again”. The only real difference is that the latter are more sophisticated, but in fairness React is also decades newer. If you try to reason through “how do I build OTP supervisors but with dozens of processes in unique roles that can retain their complex state” you will eventually reinvent React from first principles.
