Was probably a fun hobby that also earned money. They probably learned a lot in the process about how things work.

There’s a lot of transferable skills gained, but it can be hard to sell it to most employers.

Nobody cared about my hundreds of EBay sales on my resume in my late teens, but it taught me a lot:

Working with customers, how to sell and differentiate your product, managing money, managing inventory, getting cut out by Chinese competition with pricing you couldn’t possibly match...

Doesn't seem all that simple. Quite a lot of knowledge is needed and a lot up continuous upkeep. The whole article is also more or less about how it doesn't really work all that well anymore.