They didn't watch the rabbit go up the field, just followed the line of scent and were unable to make the line and carried bushing.
Just the same as a full pack of hounds would on ...say a fresh ploughed field in the wrong conditions.
There must be a lot of poor terriers out there if that's the level of your experience, I hunt all over the country with my 3 terriers and see lots of spaniel/beagle/terrier crosses out and about but nothing that comes close to a good terrier, mine are worked everyday and catch or flush to my lurcher, on average just the terriers will catch 4 or 5 bunni