>>68462698It kind of comes down to practicality and the lifestyle/culture of saplings. Saplings aren't technology oriented. They are mostly all perfectly content to just wait until they get their own way of breathing underwater (or just spending extremely long amounts of time there) instead of trying to invent some way or use the Matres to coerce the creation of some method of doing it.
An exception to this might be if we had some visitors that had no way of coming underwater with the Seisis. Then the Matres might conjure something up.
