how long they live before reproduction, reproduction rate, edibility (while you're waiting for them to be tame), in-captivity behavior, what they eat, etc matter a lot since they are the variables going into the equation for how many 100s or thousands of years you're going to have to devote to this.
Also, if they are basically useless now, most groups won't even realize there's a point to starting to tame them.
Technically, perhaps, but maybe it takes more time than a low-tech society can afford. That's close enough to untameable for practical purposes.
Why could a low tech society not afford time?
A low tech society may not have the surplus to run a wild animal breeding programme for multiple generations without interruption.
I think in this theory, it wouldn't be a program so much as it is people leaving scraps behind, animals learning that humans are a beneficial food source, and a symbiotic relationship naturally developing over time (measured in centuries).
That's very much an example of having the animal become tameable before breeding them in captivity.