Well if you subject your guitar to humidity fluctuations, it may well crack. Many do. My guild had a crack when I bought it, and when I moved to colorado it developed another. I have another guitar that has survived lots of changes in humidity and severe dryness without cracking. Maybe the wood was cured better, or I just got lucky.

I keep my nice martin humidified to ~47% all the time. Maybe it would survive dryness, but I don't want to take the chance. When they dry out it changes the way they play, being humidified properly helps keep the action consistent as well as protecting it against cracks.

https://www.classicalguitardelcamp.com/viewtopic.php?t=132051

I don't know, but here's a conversation between guitar fans about it. The wood has to be treated carefully or it will crack, I guess.

Every music store sells humidifiers because it is well known that if you don't keep your acoustic wood instruments (not just guitars, violins, harps, pianos...) at a very consistent humidity year round they will crack. If you go looking for antique musical instruments you will see a lot of them with cracks. The ones that are not cracked are the ones where the owners have cared about humidity and temperature.

Because they're made in wells.