Not that I’m aware of? Most PhD grads not staying academia seems to be a long-running phenomenon. The number of permanent academic positions simply does not match up against the number of PhD grads.
> Is that because of a culture of exploiting cheap labor?
It's not just a culture; there is a lot of government and industry grant money funding (and enabling) the exploitation in the sciences. If applied philosophy is found to be productizable and/or beneficial to National Interest, the same exploitation would grow in Philosophy departments.
Yes, in positivist sciences 20% intending to stay would be very high by historical standards.
This paper https://dspace.mit.edu/handle/1721.1/93208 gives and estimate 87% PhD holders leave before becoming (tenured) faculty. And that's academia-wide. In the sciences more will be leaving. In exact sciences yet again more.
Truth is most people leave before even getting a PhD, so it's even worse (and the advice is to think long and hard before doing a PhD, and certainly starting one because you can't find a job for a few months is sure to result in disappointment)
My dad got his PhD in the 1950s,and went straight to industry. He said it was always this way.
However there have been a couple of long term trends: Switch to gig economy for college teaching, and loss of manufacturing industry. My first job out of grad school was in a factory.