Mormon 9:20

And the reason why he ceaseth to do miracles among the children of men, is because that they dwindle in unbelief, and depart from the right way, and know not the God in whom they should trust.

The reason why he stops doing miracles among people is because they stop believing. They go the wrong way. They don’t know the God they should trust.

The reason he stops doing miracles among people is because they drift into unbelief. They wander from the right path and don’t know the God they should trust.