In mass production, especially in something still done in a hand craft scale even the experts sometimes produce pieces that are not up to their standards. Those products of lesser quality can be effortlessly discarded to maintain the standard of quality without the waste affecting much of the profitability of the production.
When you are doing something just for yourself there is no such luxury. Even when you are less experienced and skilled you usually need to produce a perfect results on a first try. Having to do it again can easily double the price when you need to acquire more materials. And you need to pay more for them anyway compared to those mass producers who can enjoy discounted prices when buying in bulk.
Considering you don't usually get to try out things it's amazing how much people still do diy things. Of course the satisfaction of having something self made is really worth it. And sometimes you can even actually save some money making things yourself. At least if you don't account for the price of all the tools. Or consider the not so perfect quality. Besides, if somebody sees what you habe done they might ask you to do one for themselves too. And then you've already had your practise piece.