It is very hard to design a good sounding box.. Years and years of research goes in to box designs and a lot of $$$ as well these days. this isn't the 70s & 80s system with just a square box with a woofer & horn. No to mention what band will want to play on a "PA hand designed and built by John Doe"?
I apolagise if I made it sound simple, I make my own and have not found it to be a difficult task. I suppose copying another design may be easier for some and so much cheaper than buying off the shelf. My latest are 2 x 12 B&C and 2" JBL horns, Bi-amped and they sound exceptional but I do understand where you are coming from