Indeed, sometimes the main reason to DIY is a creative dissatisfaction with commercial offerings. It's like making your own dinner. Yes, it's cheaper to eat at home, but sometimes you want a meal just so and the only way to get it is to make it yourself.
Of course, not everyone can cook, but if you are patient and willing to put in the effort and have good mentors you can definitely make exactly the meal you were looking to make.
For me I wanted to put together two really excellent drivers in a small two way (failed on the "smal" part! 😂) with exactly the capacitors I wanted to try out. That was my drive. It was never to undercut any retail product, but of course at a 10x markup, I don't think I would have been able to afford my speakers if found at retail.