There are multiple reasons and aspects as to why something would or would not be covered under any insurance policy.
With water damage and things related to it, if your policy doesn't cover any water damage at all, it doesn't matter the circumstances or what actions you took to prevent the damage because your insurer isn't going to cover it. Slab leak insurance coverage isn't usually so specific, either. Most slab leak damage will go under the water damaged part of a policy and everything relating to it. If it's not explicitly listed, mostly, or from an issue of maintenance or negligence (more on that below), it will definitely not be covered. This is an issue where the homeowner is usually out of a decent bit of money. Still, examine your policy. You might at least get some of the damage covered.