There are several issues that may lead to a slab leak. After all, just consider the power of moving water, which has carved canyons and caves throughout the world over time. If copper or galvanized pipes are subjected to high pressure, they can be stripped of their coating, which leaves nothing to stop internal damage that will cause leaks.
In some cases, the water itself weakens pipes. If you have a pH under 7, you have acidic or soft water, which slowly dissolves plumbing.
Some homes also have pipes made from different metals, which causes electrolysis. The different energy levels stored in each metal will react to create a current, which will cause pinhole openings in the pipe that grow larger over time.
You may even be causing a slab leak if you are not careful what you put down your drains. Harsh chemicals can cause damage to plumbing and lead to slab leaks. Failing to replace old plumbing will also cause damage.