content: Sinkholes develop from undermining of the underlying substrate like in the situation of underground creeks or rivers (there must be some void which is created below the surface for the ground to collapse into). That tends to happen when water has significant flow rate at an angle which ablates the surface of that substrate (carrying off soil). The pervious surface restricts lateral movement and only allows water to flow directly downward into the subsurface soil below it. That prevents the water from carrying off bits of soil and eliminates undermining. It is, essentially, like a coffee filter.