Sauron was never bound by the oaths Istari took, and Saruman broke his, and those involved not intervening too much. Most of the time, Gandalf & other Wizards w

Sauron was never bound by the oaths Istari took, and Saruman broke his, and those involved not intervening too much. Most of the time, Gandalf & other Wizards were running around trying to keep things together so that societies could rebuild. The remaining higher technology groups either lost the capability (Gondor), were destroyed (Arnor), are fighting constant war with Orcs with occasional dragon making problems that prevents building up proper industry (Dwarves), or are depopulated depressed groups that while not hoarding, do not interact with others anymore much and mostly use what remains of their industrial base to facilitate the last days of their race (Elves outside of Mirkwood - those in turn are trying but don't have much to build upon since Moria got overrun and they lost their main trading partner for technology). The rest is down to subsistence farming levels without base of previous knowledge to rebuild or at least inspire.