Why not just wait for the lease to expire?
Some property owners may be placed in such financial duress, they need to sell now. When that happens, they cannot sit on their hands and let debt accrue. Waiting out a lease can damage the landlord’s finances and diminishes the chances of showing the home.
If a tenant lives in a house they know is being exhibited for selling, this may create friction. Suddenly, a tenant that was just delinquent on their rent payment can now have destructive behavior. When this happens, it becomes a problem far greater than just unpaid rent.
Additionally, it can be unattractive to show a house while people still live inside. To prepare a home for sale properly, measures must be taken to make sure it looks just right. Every detail must be addressed, presenting the best visage to prospects.
By having actual residents living in a home, you are introducing an uncontrolled variable that could severely limit the opportunities for selling your home. Messy bathrooms, bedrooms, living rooms, and more could diminish the asking price, increasing stress for the homeowner.
When the lease expires and those problematic tenants are gone, the price of the house may have depreciated just because it was occupied. Now the landlord will have to tidy it up and present it anew, despite any reputation the property may have gained in the meantime.