It also has baked in social proof. Someone else found value and paid $xxx for his logo(s).

I can imagine that the good icons are taken first. But paradoxically, they are also priced the cheapest, while the really ugly icons end up being most expensive.

Strange.

Why is it good vs bad objectively? Why isn't it more suitable and less suitable for a specific buyer's purpose subjectively?

Well, in many cases a good icon can be used for many purposes.

For example, what does a whale have to do with a service like Docker? Or what does a python snake have to do with a programming language?