steering wheel keeps moving left of center

I'm a bit OCD when it comes to wanting to keep my steering wheel centered. I have a local shop adjust the alignment and straighten the wheel perfectly each time. Though I feel it goes out of adjustment much too quickly. I drive on average 500 miles a week and the wheel gradually moves left of center again in less than 3k miles. Could this be due to tire wear from the crowned roads I travel on?
Perhaps I should seek counseling instead of having the wheel adjusted each time.

Well, alignment machines don't really lie. And the modern versions with the laser reflectors are pretty darn good.

So you have to ask if the actual alignment is changing (in other words, is the before and after printout different each time?), or is something else going on like the steering angle sensor/steering rack calibration getting out (or was never reset properly when the alignment was done in the first place).

Or is there a tire issue? Swapping the front tires left to right can be helpful to determine this.