Why don't Scientists clone animals facing extinction in order to save their species?

No, they do something called sticking a male and a female in a cage and letting them get it on.

Due to high costs. However, they are storing the genomes of all endangered species in something called the " Frozen Noah's Ark." They have like 5k species so far.

cloning is not easy.   its hard.   its also inbreeding (the same DNA)

that's what i always thought.

Cloning is extremely expensive so well-structured breeding programs offer a better solution. In some cases careful breeding can "recreate" an extinct animal.

The quagga was a type of South African zebra which became extinct in about 1880. By breeding from specially selected zebras there are now "quaggas" well established in South African zoos.

The aurochs was a species of wild cattle widespread in Europe until the tenth century. It was often depicted on prehistoric European cave paintings but finally became extinct in 1627. Again, by careful breeding  very similar animals, known as heck cattle, are now well established in Holland and Germany.

high cost

Cloning is extremely difficult and extremely expensive, and for each new species we attempt to clone, we have to figure out the whole process more or less from scratch.  We're talking millions of dollars, decades of work, and sacrificing large numbers of animals to get one successful clone.  It's really not a viable long-term, large-scale strategy.  It's much, much easier to do captive breeding to keep them alive, which has the added benefit of keeping the gene pool varied.  If we reach the point where there aren't enough individuals to do captive breeding, then it's too late for clones to save the species.  

Besides, in nearly every endangered species, the problem isn't "how do we make more of them".  Nature tends to take care of that part by itself.  The problem is usually "they don't have anywhere to live, because we cut it all down and turned it into suburbs" or "they no longer have anything to eat, because we ate all their food".  Those much bigger problems aren't helped at all by cloning.

There are a few scientists and many zoos that are storing the sperms and eggs of endangered animals, so that there is some assurance that the species can be brought back from extinction if they become extinct in the wild.  Cloning is not the best way to bring back endangered animals, because clones are genetically identical.  So, if you have a bunch of clones of a single individual, then you have very low genetic diversity, and much of the diversity within the species will be gone.  Populations that have low genetic diversity also do not do well in nature because the likelihood that any individual has two copies of the same recessive, deleterious genes is high. Cloning is just as bad as excessive inbreeding, if not worse.