from below the edge of a pool, in a dogs eyes, the steps aren't at all obvious! Even normal landmarks like the surrounding garden and fence etc aren't obvious when your face is below the pool edge... They only go to the nearest edge, and scramble around. Usually the level of the pool means they cannot get their front feet up and over the edge very well, and even if they can, the edge of the pool is usually a flat surface so there's nothing at all for the dog to be able to pull themselves up against (nor can the push against anything from behind) so they scramble about and panic at being unable to escape. The panic causes them to scramble about all the more, causing them to panic all the more, and they simply drown, very quickly. Doesn't matter how well a dog can swim, if they panic they will loose energy very fast and they don't have the consciousness to simply 'tread water' until help comes...
If we had a pool, I'd do some serious training to teach them where the steps are; put large planters or something either side of the steps (perhaps with those solar lights in them or something too, in case of a night time fall!) to create an obvious landmark that can be seen from below the level of the pool (where a dogs face would be!), and do heaps of training; jumping into the pool, and swimming back to the planters/steps for a treat. Lots. Or failing that, getting one of those floating pet ramps that provides a place for them to scramble out of the pool onto and training them to use that; again with a large obvious landmark right at the pool edge for them to navigate to it.