Why are there no saber-toothed canids?

[Deleted]

There are saber-toothed cats and even saber-toothed marsupials (Thylacosmilus). Even gorgonopsids had similar teeth.

[Methane]

In the case of saber-tooth cats, those massive fangs complemented the big cat style of grappling; they'd likely wrestle down and subdue their prey with their extremely powerful forelimbs, and proceed to precisely slice and rip at their vulnerable parts (like their throats) with those teeth of theirs. Huge saber-teeth sound like an actual hindrance to canines, who rely on their mouth to grapple their prey.

[Hardcastle]

Methane is totally right. Saber teeth are what you evolve naturally when your bite becomes a "one trick pony". Cats scale in saber teeth to non saber teeth in direct correlation with the specialisation of their forelimbs to subjugate their prey. The more they can confidently rely on their forelimbs to completely incapacitate their prey, the more they are able to grow their canines into a saber-state as kill-specialised tools. Saber teeth and struggling with prey don't mix, an animal that struggles against a saber tooth, or even a longish tooth, breaks it in half. It's not practical. But a predator who can fully render it's prey subdued with it's forelimbs, can benefit from saber teeth as specialist killing tools. If it doesn't have to use it's teeth in the struggle, because it's forelimbs are so effective, then the teeth can grow. Naturally it's behaviour and inclinations will accommodate this distinction. Saber toothed cats naturally probably had their mouths shut not even looking for the bite through the struggle and melee with prey.