Why? Most sellers really do not care about cash vs mortgage. It's all about bottom line to them. At closing, the cash and mortgage deal are both cash for them.
If a seller receives several offers and the "cash offer" is low, it might be rejected. I've had a low cash offer lose to a financed offer on a foreclosure.
Every situation is different and it depends on so many things. How long has the home been on the market at the list price? Is the home overpriced? Is the home in move in condition? Does the home need repairs? Is the home vacant? and so much more...