Chashmal, your point is somewhat true, but it's of limited value and you overstate it's importance. Furthermore, you offer no explanation for why the blues has stopped evolving. The way I see it Blues morphed into R&B which later became Rock 'n Roll. While some branches of the Rock tree are decidedly non-blues, the dominate, at least commercially, form of rock for the past 20 years, namely rap, is fundamentally a mutation of blues.
I believe what you take as innovation in the past is more accurately described as artists trying to crossover to a larger, mainly white, audience. Freddie King did surf guitar music and played the theme to "Bonanza". T-Bone Walker worked supper clubs as a dancer/singer. Muddy Waters pretended he was a Folk Singer. Ike Turner was trying to sell records. For the most part current blues artist are not stretching the blues form because their audience doesn't want them to. It's a niche market and the audience wants to hear what they consider "authentic" blues. There are exceptions and I would argue that recent recordings by James Ulmer, Otis Taylor or even V.M. Bhatt are quite innovative.
I believe what you take as innovation in the past is more accurately described as artists trying to crossover to a larger, mainly white, audience. Freddie King did surf guitar music and played the theme to "Bonanza". T-Bone Walker worked supper clubs as a dancer/singer. Muddy Waters pretended he was a Folk Singer. Ike Turner was trying to sell records. For the most part current blues artist are not stretching the blues form because their audience doesn't want them to. It's a niche market and the audience wants to hear what they consider "authentic" blues. There are exceptions and I would argue that recent recordings by James Ulmer, Otis Taylor or even V.M. Bhatt are quite innovative.