The phrase "to fall off a cliff" means to experience a sudden and significant decline or failure, similar to the way someone or something would fall and crash when they go off a cliff.
Sentences with «to fall off a cliff»
As can be seen in the graph the price fell off a cliff in the past 12 months. (tallinvesting.com)
But we are not falling off a cliff when it comes to what's happening inside schools. (schooldatanerd.com)
This tablet falls off a cliff when it comes to comics, magazines and newspapers. (goodereader.com)