I recently bought a used (but working) 750W, 7 channel sound system. It put out an "honest" 120WPCH into each of seven channels, but can be switched to use just two, three, four ,etc. It's a pretty good Kenwood, cost a bit over $500 when new just for the HT receiver. I bought it to replace a 70's vintage TWO channel Marantz 2220 - that's 20 watts per channel of first generation, OTL (ie it uses bigass coupling caps to the speakers and a single polarity power supply) probably germanium transistor amp. After living with the Kenwood a few days I tore the thing back out and put the Marantz back in: it's FAR easier to use, it sounds better, and it's even LOUDER (as my neighbors will attest).
You may be happy with two inch speakers and shit that "just (barely) works" but many want something better. I'd even say most want better, but can't afford it or can't really find a demonstration that allows them to appreciate the difference. Just look at the multitude of videos on youtube, the deadtree magazines devoted to higher end stuff (tho I never even said Radio Shack sold "higher end" - in fact I said AFFORDABLE higher end, which is more like mid level) and the people willing to still pay dollars to go see movies in theatres -- where they can enjoy the sound without worrying about pissing off the neighbors.
ANd if you build anything nowdays you'll end up using SMD for some of it. That shit is mad difficult to solder, especially if you're over 40. This is why so many "kits" come with parts of pc boards already soldered. But what do you do if you design your own kit? Now you gotta track down a service. It would take less than 5000 worth of machinery at a location to be able to do this. Would they all make a return? Nope - but plenty in select "pilot" locations would net enough return to pay for an expansion in store coverage... just like those cellphone things they've been so stuck on these last years. And a whole lot more of a captured market.