For me, it's part of archery. Making what I can gives me more enjoyment of the sport. Most of the time it would be cheaper for me to buy at first but I do it more for fun than savings.
I've been that way with every sport I've taken up. Reloading, making cast bullets and accurizing my own firearms when I was into that.
When I took up black powder it was casting balls, making patch lube and then on to building rifles.
As for archery, I've started a self bow but will have to try and finish it this winter when I get some free time but do enjoy making arrows, strings and quivers. It just adds to it for me.
Some folks don't like making arrows, strings and other things and there's nothing wrong with that. I myself, enjoy it.