Why would a gunite pool have a vinyl liner?

A very limited few were intentionally built that way. Usually in very low lying areas where cement/vermiculite allowed too much water to come through, making it impossible to "seat" the liner. However, this scenario does apply more to concrete than gunite.

Gunite pools have a very short life (less than 20 years) of troublefree enjoyment, then the cracks, leaks, stains, and algae take over. Pool owners try either paint, epoxy, or new plaster. None of these solutions last more than three to four years, then they are forced to start over seeking a solution.

Then, along comes a liner salesman with, what sounds like, THE answer. They will nail a "bead receptor" around the top of the pool, then install a beautiful, long lasting vinyl liner into the pool, with a 10 year warranty (pro-rated by the way). These pro-rated warranties are a bad joke, as every vinyl liner pool owner already knows.

Nevertheless, after the last debaucle with two-part epoxy, plaster (marcite), or paint, this sounds like the obvious answer. Unfortunately, it is the worst answer of all! It won't even last three years. The bead receptor must be a part of the concrete deck around the pool, it can not be, under any condition, added later.

That is why a gunite pool could have a vinyl liner.