Why were many types of crafts and arts forgotten during the period of the Horde invasion?

The main reason is the death of artisans during the devastation of cities – Ryazan (1237), Vladimir (1238), Kiev (1240), as well as their hijacking to the Mongol Empire to work. Another reason is the general impoverishment of the Russian principalities, after all, not all cities were ruined (Novgorod, Pskov, Polotsk escaped this), but poverty increased, so crafts were forgotten and even stone construction stopped for several decades.