Blame the magicians!
Thousands of magicians and nearly the entire amount of literature died in the flames Bleagurs. Few skilled magicians had not followed the call of the city, and so magic almost disappeared. The few that remained were not understood and those who are not understood are pursued. Be it the unsuccessful hunt or the bad harvest, magicians have always been found guilty. The last remaining scriptures burned with them in the flames of the pyres.
For a long time, magic could only be done in secret. And the knowledge of magic disappeared almost completely.