You left out one of the biggest causes of this. For many people in that 56%, the year they end up in the top 10% is the year their last surviving parent passes away. Inheritance is a big one-time windfall for many people.

The other misleading thing is it looks at 44 years of longitudinal data, and doesn't make corrections for differences between the early years and later years. Income has become more polar in the last 40 years, so the current numbers are a fair bit worse than the average numbers of the last 4.4 decades.