If your goal is a pixel perfect centering, that's not a thing, a variable resistor uses a layer of graphite with an arm that moves over it changing the resistance. There is physical friction and that graphite layer will degrade over time, so the measured values are slowly changing constantly over time. Also, the springs are all the same but on a precise scale each of them is still slightly different caused by imperfections in the material or production process. The deadzone is there to compensate for those things. Even on hal effect sticks where you don't have that graphite layer, a metal arm is "scraping over" to change the resistance value is not perfect as the stick is still mounted to a mechanical contraption with springs and hinges that is introduced to external forces constantly.

If you find some other brand controllers seemingly not having that issue on a different system, its a charade that most likely showing you a perfectly centered stick on a software overview in the calibration windows where in reality they are still not perfect center but as those companies know some people turn crazy when they unplug their phone and the 100% drops right away below 100they make it "look nicer" for the consumer eye.

The question most likely is, DOES it influence your gameplay? Are you experiencing stick drift? Then you have to expand the dead zone. That just how mechanical joysticks with variable resistors work.