>Why would expenses need to track less than inflation, if your wages are tracking with it?

Because wages don't go up in real time so you get robbed of the difference for the duration.

You make $3. Rent costs $1. You have $2 leftover to improve your life, pay down debt, whatever.

You make $3. Rent is now $1.50. You have $.50 leftover

Your wage goes up to $3.50. Rent is now $2. You have $.50 leftover.

Repeat a bunch of times.

Your wage goes up $.50 again. Rent stops rising in price. You have $1 leftover.

See how the inflation robs you of $.50 multiplied by the duration?