When the Explorer skill tree was designed, the level cap was still 50 and the expanded content hadn't been added yet. Most of us who were already 50 or close to it when the science system landed, skilled our specialists for the highest level of searches because we don't generally use the lower levels except in very rare circumstances (like when an event asks us to 'find x event rewards' with a specific search type). So we skilled up our Explorers with the abilities that affected the Very Long Treasure Search because it was the one that we were going to use at the time. Then the level expansion came along and with it, the Prolonged Treasure Search. Not only is it a lot better than the Very Long search, it's also often better than the special searches unlocked at the top of the Explorer tree. So, those books that we invested thinking they would be useful are now sitting unused. Because those skills are towards the top of the tree, resetting them is unbelievably expensive either in lost books or gems, especially as we normally have a lot of Explorers.

Could the skills that affect Very Long Treasure Searches also affect Prolonged Treasure Searches where appropriate? I don't think it's possible to find Exotic Wood on a Prolonged Search, so the Deforestation and Mistwalker skills don't need to change but the Sabbatical and Streetwise Negotiator skills should also affect Prolonged Searches.