answer:For the most part, those species that we have domesticated have demonstrated that they meet multiple criteria to varying degrees. They provide a useful function or product, they are willing to breed in captivity, they are reasonably safe to work with (placid temperament and unlikely to panic), have an easily supplied diet, and have a reasonably fast growth rate. The number of non-domesticated species that fit all of those criteria to an acceptable degree is actually pretty small. The ratio of value to cost makes it not worth the effort. (While some of those features can be adjusted to some degree by selective breeding, the basic benefit must still exist.) It could be argued that ostrich and emu farming, bison herds, and captive salmon production are examples of domestication-in-process.