From my reading of heat pumps, mismatches in energy sources and sinks can make linking things together more complicated (aka more expensive) than is commonly available.

For the pool <-> A/C case, This Old House did a segment on linking the systems: https://www.youtube.com/watch?v=J7fB8ul9dZw

Edit: chris_va has more details about why linking systems is hard: https://news.ycombinator.com/item?id=23001888