Python and Ruby are extremely malleable, like Smalltalk and lisp before them. You can inspect anything, you can override / replace / proxy anything. You can use a few built-in collection types for nearly anything.

This is by design. This is great for prototyping.

These languages are to programming what breadboards and wires are for electronics.

Of course, as your system grows, you start to want static checks, or having your schematics on a PCB. But at the very start, tweaking a piece of Python code, or a breadboard, is easiest. Then, of course, you may not want to afford a a rewrite to rust, or would put your breadboard in a box and ship it :)