Because after twenty years of it your body will be wrecked.

I work in IT and have multiple coworkers who actually work physically harder than I do (in their roles vs. mine) in their 60s. One is 65.

Got lots of 65 year old factory or construction workers, do ya? And I’m talking about laborers, not supervisors etc.

This is silly. Absolute worst case, we go back to bartering for goods and services. There will never be a need to panic.

Then you should talk to a professional until you feel differently. This is not normal. Being smart is good. Being curious is good. Being a lifelong learner is ideal. Whoever or whatever taught or showed you otherwise is wrong.