Speech therapy doesn't work for all stutterers. I have a very severe stutter and it's likely neurological - it happens in every situation, every day, and I've had it since I was a toddler. I'm now approaching my mid-30s and speech therapy has never worked for me. At its root, it's a speech-motor control disorder that for many of us, we can't simply "train away" no matter how hard we try (just like how the deaf or blind can't suddenly start hearing or seeing normally by "trying harder"). It's actually quite offensive to insinuate that those with severe stutters are the way they are because they don't "try hard enough".