There’s a few reasons why there was no fence on the property:
1) Not all cities, towns or even neighborhoods permit people to put up fencing on their own property.
2) The dogs’ owner may not have been able to afford to put up a fence.
3) The dogs’ owner may not have wanted a fence.
Of course, these reasons are not mutually exclusive and the answer may be a combination thereof.
I’m talking about the moral responsibility of the owner. He created the stage for a tragedy.
1) Don’t get a dog if you’re going to chain it.
2) Don’t get a dog if you can’t provide a safe fenced home.
3) Don’t get a dog and leave it unprotected where other dogs can get it.