I can think of a few reasons of varying quality not to introduce agriculture in no particular order.
1. Agriculture, or rather, agriculture large enough to sustain cities, usually comes with a large degree of necessary social stratification. I have heard of a few societies in human history that managed to have cities without institutionalized social inequality but these examples are few and far between. I don't believe that the agricultural revolution is ultimately responsible for all of humanity's sins, but it is responsible for creating societies with large populations. And in societies with large populations it becomes easier for the ruling elite to see their followers less as the people they are charged with leading and protecting, and more as pawns that can be used for their own ends. I admit this might be a bit of a stretch, but there are other good reasons not to introduce agriculture.
2. As mentioned before, agriculture does indeed tend to produce large populations in comparison with other societies. But this takes a while, likely more than one lifetime before there is a significant difference in population compared to previous years. Even if Taiga does want to introduce agriculture, the benefits of having a large population won't exist till Taiga is old and gray, and I doubt Taiga thinks the war will last that long.
3. Although the benefits of switching to agriculture are delayed, the costs aren't. Teaching his people agriculture would require more people to stop doing whatever they are good and practiced at. Which wouldn't be terrible if not for the fact that Taiga's people are in a war for their survival right now. Although you can make a strong case for war inspiring other innovations, I don't think agriculture would be high on the priority list for the reasons mentioned above.