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For the same reason you avoid inheritance in non-dynamic languages.

Inheritance is the strongest coupling relationship. Often times too strong, inflexibly so.

What you're expressing is that the child class must have an is-a relationship with the parent.

Otherwise it violates the Liskov Principle.

My incomplete but practical 2-liner is this:

The child should be perfectly substitutable with it's > parent, with no change in behaviour; meaning no errors and > no incorrect-behaviour in either.

This isn't an abstract rule, it has practical repercussions:

If Class A has an is-a relationship with Class B, you, or (most likely) another person that got convinced by your is-a assertion` of that relationship will be tempted to write something like this:

class Animal { 
  backLegs = new BackLegs()

  move() { 
    this.backLegs.move()
  }
}

// this is OK
class Dog extends Animal {
  frontLegs = new FrontLegs()
  move() { 
    super.move()
    this.frontLegs.move()
  }
}

// this is not OK

class Fish extends Animal { 
  frontLegs = null
  fins = new Fins()
  move() { 
    super.move()
    this.moveFins()
  }
}


// Now, you got a mixed array of items, some `animals`, 
others are `plants`... 

// we know all animals can move so:
items.
 .filter(item => item instanceof Animal)
 .forEach(animal => animal.move())

// Reference Error: cannot find frontLegs on Fish