It is unfair and sad, no doubt.

However, it all comes down to supply and demand. It's a reality.

If a shelter or rescue has space for only three dogs, they would be wiser to take the three dogs that are most likely to find homes in a reasonable length of time. Given, of course, that they have good temperments, etc.

A simple mathmatical example ... if you pull three highly adoptable dogs from a kill shelter, and those dogs find homes in a week, then a week later you can go back to the kill shelter and pull three more adoptable dogs, etc. Therefore, in a year you have saved over 150 dogs from death.

OTOH, if you pull three dogs from the kill shelter the first week that are difficult to place ... size, color, breed, whatever ... they may not get adopted for months. Yes, you've eventually saved three dogs that would otherwise die. But, in the mean time, in the three months it took them to find homes, 36 other dogs died while the space was occupied. So, you might end up finding a home for twelve dogs instead of 150 during the course of a year.