It doesn't. The BEA invented the PCE for figuring real personal income growth so they can include all consumption prices --not just urban comumer purchases; since '80 it's averaged 1.44%. My plot with CPI adjustments is useless for anything beyond showing a comparison with the PCE. The BEA uses the GDP deflator to get real GDP so they can cover prices over the entire economy; the deflator is the broadest inflation measure and it goes far beyond even the PCE.
That's just what the government does. The question of why it's doing it is more of a question of what the people want, and what I want is to know how to plan for the changing market place. I've gotten rich assuming people's incomes are growing.
I am glad you have done so well for yourself. Now, ask yourself, is your success because personal income has been growing at .9% per year or because the ability and willingness to borrow has grown at rate commensurate with the growth in household debt, which has unarguably been soaring?