Also for dogs, the only difference between the 3yr and 1yr vaccine is the cost, and they last longer than 3 years anyway.

So a lot of owners will get it once or when needed for travel or something. Because ya, animal vaccines are not as well studied as human ones and are used across a higher diversity of breeds/species/ages. Like with covid children under 3 had to wait 2 years before studies completed, while I'm pretty sure the standard testing dog is a young beagle like in the study I linked.