Why should the owner pay for background checks? By requiring prospective tenants to pay for their own applications and background checks landlords dramatically reduce the number of people with credit problems from wasting their time.
If applying were free what would prevent people with serious felonies and financial problems from applying to any and every rental? Nothing at all.
Also, it can cost $50 - $75 for a proper background check. Imagine how expensive that could be for a landlord.