Moreover, if one wishes to completely eradicate the magic path, inevitably many sects of justice will transform back into the magic path.
There is justice and there is evil. As the saying goes, solitary yin does not grow, solitary yang does not survive; if all evil is defeated, then some people among the righteous will gradually become depraved and slowly turn into the new evil.
Of course, this is not the true reason why they don't completely eliminate the magic path. The real reason is that if they truly eradicate the magic path, the existence of the people they've fought for would be questioned. At that time, they would retreat from the world, becoming legends and ignoring worldly affairs. But if a new magic path arises then, they won't be able to quickly eliminate it, resulting in a longer period for those in the magic path to roam free and cause more harm.
