Unless there is massive population growth. Single older person can employ only so many juniors. Or other older people have to exit the market.

It's like a MLM spread across generations of workers. You recruit two workers and they recruit two workers each and then they recruit two workers each....

If you spend 2/3 of your career as one of the 2 underlings it's not MLM. Body is dunzo by say 50 for trades, which means you get 30 years as a tradesman and 15 years employing two tradesman. Retire at 65.

Or there's an increase in new buildings, or the number of buildings needing repairs increase over time, etc... With trades the number of self-employed or owners is quite high - you can either do Job A by yourself for $X for company Foo, or be self-employed and do Job A by yourself for $X++. Same number of jobs exist, just less monopolized by larger companies. I don't know why, but this is what I found in the south-west of England when I lived there. I think the experienced people tend to start those orgs to charge more then get older and need to hire apprentices to do the work for them, and so the cycle continues.