A cataclysm of arcanic energies causing a rift between the fabric of ether and the reality of Torill.
The planes pushed away by the explosion of strange powers, caused the gods a weakened state from which to incur their wrath upon the planar.
For those who don't know, in ancient times of Forgotten Realms canon, there was one world, Abeir-Torril.
You may have heard of this world, in it's split form of Torril, brother to the planet Abeir that split off during another unrelated cataclysm.
Lots of those going around.
So we now have two worlds and a disconnect between them growing larger and larger as something is consuming upon the world of Torril.
The people can still reach and manipulate their gods powers, but communing is rare, and those who can do it are powerful for they're breaking through whatever veil is causing the disconnect.
Those in areas of low magical resistance may find it easier to conduct their craft in service to their deities.