When you made a ready-made commercial product, you pay for tax burden in various stages of the manufacture:
Moreover, to buy the product, one has to have money, which are usually got from employment. When the employer pays the employee, there is an additional tax burden.
If someone builds a Ronja, his time is not first sold to his employer, then taxed, and then taxed again when buying the commercial product. Instead he cuts straight through all this and invests the time to build Ronja directly, which is of course not subject to a tax. This way some taxes are saved.