I mean, for an almost 10 year old game it's almost a miracle that it still has the numbers and community surrounding it and that is without updates for years now.
There was a thread years ago (I think 2014-2015?) on here about how the game is dying and how it will become a wasteland in the following 1-2 years. That really didn't come to fruition, thankfully, but it shows how much people overreact to even a small dip in player numbers.
Still, even if the game "dies" then there is no point in fighting against that much, since it's inevitable. Although, who knows, maybe after 3-5 years there will be a renaissance of it, just like what happened to Minecraft. I know it's not a great comparison but still: it was huge in the early 2010s, had a negative stigma it was associated with and subsequently stagnated/"died" in around 2015-2016, then became popular again in 2019/2020.
I mean there is technically a "solution" (well, more like a bandaid) but it would require a lot of money, a lot of patience and it's not exactly foolproof: buying keys/gifts of the Warband DLC Collection (includes NW) or just the NW DLC and mass distributing it on a giveaway site like SteamGift/just giving it away to someone on your friendlist. It's not a guarantee they will actually play in the comp/reg scene or even NW, but it would be probably increase the amount of people playing Warband in general.