Somebody in the past has left the house unheated for a week or more, and the pipes froze, causing them to develop cracks (as shown in your photos).
Mmm.. one other, extremely remote possibility: excessive water pressure. This would be far more likely to result in leaking fixtures rather than burst pipes, though.
Still, if your house is near the bottom of a valley or something, the water pressure might be a tad higher than normal.
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