Simple, the internet, ruination of terrier and lurcherwork. The last maybe 10 years especially.
60's 70's and into the 80's collie x's or lurcher x lurcher with collie on both sides would've been the predominating types for all lurcherwork, with deer/greys or beddy/greys in certain areas a close second.
Not having a personal dig at you, but there have been, and still are some very powerful efficient fox killing collie x's around that love the job. The fact you've not seen em doesn't mean they don't exist, or that you need a bull x for the job