Putting a dog on a chain is something that we see a lot here, and although at first I was very adamant ALL dogs should be unchained, there are situations now where I understand the owner. The problem is we always focus on the bad cases, and not the legitimate reason why a dog is chained.
There are many Canarians that love their dogs, and education has meant that chaining is normal, and often they use the pully runs here, which I found very clever. These allow the dogs to run around the property, but not leave it.
As an owner of two dogs that love to escape I know how hard it is to keep a dog in when they want to get out. I don't chain my dogs, but I also spend most of my day screaming "get back in here arseholes", at them .
Before, anyone jumps on the all dogs can be trained to stay in an area, some can't. For some owners, chaining the dogs so they remain on the property when they are not there is the only option. Many owners don't live on their fincas, therefore, when they leave they want to know their dog will be there, when they return.
As with everything in the world, you need to look at all of the facts, and speak to the owner, to see why they chain their dogs. Every situation is different, and for some people we need to help to educate them on other ways, not just jump down their throat and declare they are bad owners.