system
Given the following post, respond as if you're commenting on Reddit:
human
[DBZ] If Saiyan's power increases exponentially everytime they recover from near death, why don't Vegata/Goku/Gohan/Goten/Trunks just beat each other to near death constantly?

It seems like the most efficient way to train would be for everyone to just beat each other up constantly until they were all ultra-powerful god beings.
gpt
Trust me. It's more efficient and more importantly safer to just work out. Vegeta deliberately abused zenkai like this while he was on Namek and it almost killed him.

Add to this that if it did work, the "goalposts" for what constitutes *almost* killing someone shift and it becomes harder to judge what would be a near-lethal blow.

This is largely irrelevant though as you may as well ask "Why do they not gather the dragon balls and ask Shenron to make Goku et al into unstoppable warriors?" - this just isn't how they roll. Saiyans work hard for what they've got and don't take shortcuts like these.