Fair. But, like a lot of these things, economic home production probably also requires a fair bit of production/use. My problem was that I just wasn't drinking enough and my scoby ended up contaminated.
Yeah, if you use a lot and are just producing unflavored, kombucha is pretty easy/cheap.
Kombucha is the exception.
I make kombucha at home. The labor is extremely minimal (basically the same effort as making a gallon of sweet iced tea) and the economics absolutely make sense - the cost less than $1 a gallon for me to make it vs $3-5 for 16 oz at the grocery store. Plus I already have pounds of tea at home.
The other reasons I make it are to avoid having to haul heavy bottles into the house and because I prefer unflavored kombucha and only flavored ones are widely available commercially.