I get they're going for a mortar and stone type idea but the availability of sap makes this prohibitive at minimum. And the quantities needed of sap for even a small stone hut make it virtually pointless.
If sap were either yielding more I could see the encouraging trade and raids argument. Or if it were less rare I could understand the basic inclusion. But being both rare and low supply, as well as being a basic necessity for so many items its hard to picture it being functional for anything but the conglomerate companies that already have most of the sap locked down anyway.
