FIxed length track bars pull the axle over because the track bar is connected to the chassis on one end and to the axle on the other.
Like the angled diagonal line in the letter Z. When the upper horizontal line of the Z (the Jeep chassis) is lifted up by a suspension lift, the track bar (diagonal line) pulls the lower line (axle) over sideways. Installing an adjustable length track bar is the only fix for that issue.
Backspacing is the distance between the rear edge of the wheel and its mounting flange as is being measured below by the yellow tape measure The more backspacing a wheel has, the further into the wheelwell the wheel and tire is positioned. Factory wheels have a lot of backspacing to keep the wheels form sticking out too far. Aftermarket wheels generally have less backspacing so they protrude out further. I like to have as much backspacing as is possible without it causing the inside of my tires to rub on anything.