One of my non-knitting friends recently asked me why am I so interested in making clothing.
I've been sewing and knitting since I was in my teens. I was heavily influenced by my mother who sewed, knit and crocheted. People become garment makers for many different reasons. Some of us want unique garments, some have special fitting problems, others just have a need to know how the magic of garment creation works and love to learn all of the techniques required. We have a need as humans to adorn ourselves, it's a form of artistic expression for many of us even when we don't make the clothes. Just check out the outfit pages in Pinterest to see how people are using clothing as self-expression.
Some garment makers have very little interest in current fashion and take a more historical approach to their learning path. You see this with knitters too. We keep Fair Isle designs and specific lace traditions (Orenburg and Estonian) alive when they would otherwise disappear.
Why am I doing this? I can't not do it!