They don't. Go look up random players that you know and the deviations are wild.
Juan Soto has an xBA 20 pts higher than his BA.
Jose Abreu has an xBA 9 pts lower than his actual average.
Bryan Reynolds has an xBA 14 pts lower than his actual average.
Andrew Vaughn has an xBA 18 pts lower than his average.
Josh Donaldson has an xBA 9 pts lower than his average
Elvis Andrus has an xBA 13 pts higher than his average.
Matt Olson and Ronald Acuna have an xBA 8 higher than their average.
Giancarlo Stanton has an xBA 28 pts higher than his average
Kyle Schwarber has an xBA 21 pts higher than his average.
Guys that I looked up that matched(greater than or equal to 5 pts)
Harper, Ohtani, Rutschman, Torres.
Judge was 6 pts different.
Large enough sample for you?
xBA is ok for QoC and on individual batted balls, but does not hold over a full season.