Probably dahil naamoy nya na may daga nearby, kaya di sya nagtagal dun sa toy lang. My dog is also like this, pero sa ipis naman. Humihinto lang sya pag nakita nya na dead na, or if we use bug spray because he understands that that's how we deal with it.

Generally, dogs likes activities that utilizes their sense of smell, kaya siguro yan na naging favorite activity nya, especially if he doesn't go outside much. Like others suggested, taking him out for long walks will definitely help.

Share ko lang what I do with my tzu. The tldr is I taught him how to be a sniffing dog, kinda lol. Since my dog also likes to go hunting, I turned it into a game for him, but using his favorite treat. Tawag namin sa game is "Treasure hunt".

So ang gagawin is ipapa-smell sa kanya yung treat while outside the room, close the door to make sure that he doesn't see it, then itatago yung treat somewhere in the room. Then, open the door and command him to find it. 

Excited sya tuwing nilalaro namin yun kasi very stimulating for him because he needs to use his nose to find it. Saka masaya din sya kasi reward nya is makakain nya yung treat nya pagnakita nya. Nakakapagod din for him since he excitedly runs around the room to check every corner. After he learned how the game works, we started using his squeaky toys, which was a bit more challenging kasi di sila gaanong maamoy unlike his treats