I've been selling them fairly steadily when I list for pebbles. MS wolves will sit for awhile, sometimes they sell if they're quite pretty or rare genes.
I don't really play other breeding petsim games besides FR, but honestly I think part of the problem is how short the breeding cooldowns are. I think they do vary per breed rarity, but for example bracchus are 10 days. On FR, the most common breeds are 15 days, and each incubation requires an interaction over 5 days. I've been feeling like it's just too easy to breed wolves here, and I already have a massive collection from largely my own puppies. Combining with being able to make as many wolves as you are able be expecting at once, it just has really exploded.
Definitely though, the biggest problem with wolf population is that releasing doesn't give enough rewards.