I can't see how to make this question any more specific, so with that..

Lack of skill and/or resources and opportunities. I cannot smelt iron ore and forge my own forks.

An rather pointless thing to hang on to in the grand scheme of things.

Cost-benefit considerations: for great many things it's much cheaper (in terms of money, time, and effort) for me to buy them rather than make them.

I did not mean you have to do EVERYTHING yourself but there are things that you can do it and they do not take a huge amount of effort.

Also, fun theory.