We have been running our CNC daily for about a year and a half. Two of the three motor belts were almost completely worn through and the third one was well on the way (see uploaded picture)
I would check the alignment.
My belts are going on 5 years…
Also, when was the last time you replaced your pinion gears? You should be going through those about as fast as the belts. I would be interested in seeing the numbs left on those bad boys 
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The machine I bought is experiencing the same as @subnoize , the belts are coming up on 5yrs (in December) and they are still the original factory set showing very little wear.
We have never replaced the pinion gears and they look in decent condition.
Yet all three belts have needed to be replaced. I will look into the alignment. Thanks for the suggestion.
Those don’t look like wear to me, more like seperation due to too much tension, or possibly defective belts, or maybe some other mechanical problem (like alignment mentioned above). Like others have stated, mine are almost 5 years old and look great. I’m not in production, so my use is pretty light, but I have done a quite a bit of laser rastering and 2.5D carving, and my X belt is just fine yet.