I fail to see the point of paying housing benefits to the tenant instead of paying them direct to the landlord.
Paying benefits directly to the landlord would be 100% effective and timely. It would remove the possibility of the tenant using housing benefit to pay for other things, and remove the temptation to do so. Giving a person with financial difficulties money is simply asking for trouble.
Even if tenants receiving the benefit payments themselves were 100% reliable and always passed the payment on to the landlord as rent, it could never be as efficient as paying the benefit directly to the landlord.