I wonder why this region has so few mammal observations. There are only 18 mammals documented in this region. Is it a lack of observation, or are some animals just too rare to find, like tigers, leopards, lynxes, wolves, and moose. The observations we do have in the region are good and do offer some insight as to what inhabits the area.
Probably depends a lot on the users in the region. Different users often have different niches they specialize in for observations, even if unintentionally.
Additionally, mammals are often harder to spot (and photograph) than people think. The majority of mammals tend to be small, many are nocturnal or crepuscular, and most are wary. We tend to have a biased perception of mammal sizes, distribution, and activities based on the few large animals that we do see, which are often ones that are seen in groups as well.
When it comes to the predators (4 out of the 5 species you mentioned) those numbers tend to be very low even in undisturbed ecosystems because it takes a lot of of other animals as food to feed just one predator.
May be there are not so many mammal observers on the iNat yet? There are mostly plant- and birdwatchers who active in the photouploading.
PS: If you are interested in Russian mammals you can try to use http://rusmam.ru/, the DB of Russian Academy of Science.
Primorsky Krai seems in fact to be special, in having some very active botanists! Top 50 are: 47 plant species, 2 fungi and a single bird species. Top observer is Surovtseva Natalia, she made more than half of all observations in Primorsky Krai within the last year!
There are some avid mammal watchers on iNat, but it seems they were not in Primorsky Krai until now see e.g. https://www.inaturalist.org/observations/pfaucher