Looking through maintenance records I see that in an aircraft like an A320 (for example) on average, tires get replaced every 3 months due to regular wear and tear. The limit for a serviceable tire at my company is 2/32″ (inches) below that, the tire must be replaced at the next service check.
However tires get replaced all the time for other factors, for example a tire that was recently changed could have cuts or cracks because they may have hit something (FOD) in the ground while taxiing or taking off. Depending how deep is the cut they may need to be replaced before next flight. Also another reason is due to tire air pressure. We check pressure very regularly and if is below certain limit it must be replaced, or if a tire was serviced and then couple of days later requires more inflation it indicates that this tire is leaking and need to be replaced. I hope I have answered your question. By the way this is me after finishing replacing an A330 tire.
This is how a new (or recently changed) tire should look like: later on my next tire change I’ll update the answer with a picture of a worn one.
Worn tire after so many take-offs and landings.