DIY versus Brand Name Speakers

Let me state at the outset that it is not my intention to stir a hornets' nest. I simply wish to gain a better understanding of the logic that informs a decision to build your own speakers as opposed to buying them from your local dealer.

I have followed the DIY speaker projects on the forum with much interest, admiration and envy. However, I was wondering whether homemade speakers are significantly better sounding than mass produced speakers at the same or similar price? To contextualise my question, allow me to raise a few issues. A company like B&W, for example, has millions at its disposable to invest in testing facilities, R&D and skilled technicians. Large speaker manufacturers can also reap the benefits of economies of scale. If it was possible to produce brand-beating speakers in your garage, would we not have seen a massive proliferation of producers flooding the market? Does the same logic apply to other mass produced goods? Would anyone buy a DIY car or television?