Everybody poops.
The same goes for carpenters, masonry, etc. The physical work will wear you down — but by the time that becomes a problem you should be skilled enough to be a manager.
I'm making decent money now, but it's crazy how much trade work was frowned upon when I graduated high school. In retrospect I think I'd be totally happy with being a contractor managing a small business.
I've also hired tradespeople who did put in the time and were worse than doing the job myself after watching youtube videos for a few hours, so at that point what's it even accomplishing.
It doesn't necessarily mean that it takes any more or less effort or intelligence to finish a university degree.
It also doesn't mean that average intelligence is dropping.
It just indicates a stereotypical reversion to mean.