This is based on the Department of Finance's projection of different types of income sources, for instance, dividend income, capital gains income, and, ordinary interest income or wage.
The $200,000 bracket will be indexed to inflation, however, these sources of income tend to have growth rates beyond inflation. There will be what we call a bit of bracket creeping, that is, individuals who would see higher tax being paid just because their sources of income have increased at a pace that is greater than the indexation, so they will pay a bit more. Therefore, the acceleration factor you may see is in part due to that aspect of the methodology or the assumptions.