Why DIY? - for multiple reasons.
The first and main reason is because we can. Why enlist others to do something we can handle? We can do the majority of the jobs or projects that come about because, well, we are handy! We also derive satisfaction out of fixing something or completing a project on our own.
DIYers are also particular. It pains us to pay someone to do a job that we can do as good or better than some contractors. We are also cheap (frugal is a better word). In some cases we can complete a job at ⅓ rd the price we would pay to have it done.