That's how much time can be lost to ineffective reading skills. The second reason is that nobody believes that anything can be done to effectively help in this area, especially when it comes to technical reading. I've spoken to some of my people and they feel they read well enough. They say they're faster than most. Most people have no idea of their speed or comprehension.
Most people only compare themselves to other inadequate readers.
Even if they are twice as fast as their co-worker, that's still very slow when compared to even our lowest performing graduates. Also, their comprehension and recall is probably a third of what they think it is. That's where a big impact is on their productivity. My answer is always conservative, so there are nice surprises later. Whatever your problems and deadlines, I have to believe that 20,000 hours would have to make an impact.