Wages are literally income. Income is money that comes to you.
So a businessman invests money, makes a business, has an income from it. He gets to deduct the cost of the buildings, the facilities, transportation, and write off the wear and tear on machinery. This man is deducts all before profit.
A man goes to work, everything he is paid, is considered income. In short, the equipment which is his skill, mind and body are non deductible, although they are finite. He is chattel. Wages are not income, it is a straight trade for value. Like purchasing his time. This is time he can never get back no matter how long he lives.