Who says they didn't try? The Vargr were just the species that worked decently (there's evidence that the Ancient that were playing around with them still was tinkering with them when he got it in the neck) and survived for 300,000 years. IMTU there's another uplifted Terran species (otters) on one of the worlds in Foreven. It's just that being a minor race, they never got the press that the Vargr got. Any failed experiments obviously disappeared without a trace, and even successful experiments could easily have gotten wiped out during the Final War.I think the Vargr as Ancient uplift scenario is kinda lame and far-fetched. What the hell would Ancients care about wolves for? So many other mammals out there. Why not dolphin- or whale-people? So Vargr will be bipedal pack-minded sophonts with no resemblance to wolves.
In short, there's no reason why the Ancients had to have any particular regard for wolves (proto-canines) over a score of other Terran species. Most probably they just got lucky.
Hans