The simple factor is that, as seen with the wide variety of creatures present in the Rampage, the region generally presents greater competition that forces the Kamuran Arzuros to not be able to rely on foraging as much as their Yukomo or Moga counterparts.
The greater amount of larger predators such as Zinogre, Rathalos, or Lagiacrus in its more common habitats make Arzuros prone to foraging in, well, forests rather than open spaces where its more at risk of being picked off. While the Kamuran subspecies still retains some of these predators, and even gains new ones in monsters like Magnamalo and Bazelgeuse, it is actually the greater variety of creatures around its own ecological standing that present the most issue.
Monsters such as Bishaten, Great Izuchi, and Aknosom present new competition for Arzuros in terms of foraging rights. The smaller and faster opportunists able to nab up the good fruits and honeys before the Fanged Beasts can get to them first. As a result, the bears have refocused their hunting instincts in order to compensate. Hunting while its contemporaries are foraging, and then foraging what's left once they in turn go hunting themselves. To note, fish, Bullfango, and Gargwa are recorded to make up a greater quantity of the Kamuran Arzuros diet than even Yokomo Aruzros, despite both habitats having relatively the same prey resources.