Because they are completely passive, need 11 people less than workshop, are very cheap to build and usually turn profit after 5-20 days (depending on food price and gardener), if you skip the last upgrade.Why waste space on garden ? Try building 4 workshop with everything upgraded . After 100 days I'm getting near 80+ k from 4 workshops selling knives. Invest early in that two sister ,u can buy iron and wood 2 bucks child paper than market price. That storm child,averri or whatever that redhead girl,Another captured slave with high intelligence(forgor her name too ),aria/Caitlin with decent intelligence - make them your foreman and mailynn as head maid for her high discipline. Only 3 men in whole 80+ household,currently swimming in money and ladies!
But, they are obviously nowhere near the profit margins of going all in on workshops.