It implies a hierarchy - some are stronger, faster, in better shape than others which goes against the modern Left's Harrison Bergeron ideal of absolute equality.
It also heavily focuses on discipline and self-improvement, both of which are anathema to the Left.
It is individualist vs. collectivist
There are many other reasons like the lionization of weakness, reliance on authority, oppression olympics, etc. The gist is You are bad, We are good. Requires some torturous mental gymnastics but that is the state of the Left.