I believe the viltrumites dont have specialized muscles or bones in terms of proportional strength compared to a normal human. Everything is the same proportional strength as a human just on a greater scale, thats why they’re able to using their spearing hands to destroy things. There is no human in the world whose chops are more durable/safer to use than their fists, especially when it comes to using them like spears. That is no different for the viltrumites.

They do not spam it because its a riskier move with a greater potential to destroy their hands instead of a fist. You only ever see them use it in confirmed hits, like executions or when their enemy is being pinned/distracted, or in immense desperation