The biggest reason as to why it is so popular on native and not on NW is the ease of the GF server on NW. If you just wanna play groupfighting for an hour or so you could either: A) sit in a queue and pray that other people will join in. B) hop on the gf server for a bit and just play the game instantly.
Yes, proper 6v6 is perhaps more enjoyable than the chaos and randomness of the gf server. But on the other hand, when I just wanna play this game for a bit I often just wanna fuck around on the gf server and do quick melee. Just run in, do some shit, die, repeat next round. There's no downtime, there are no queues to miss, there are no obligations towards ur teammates to play properly. You can just play the game for a bit.
WBMM was fun for a while, until the novelty of it and thus the reason for tryharding for ranks wore off. From then on it was simply more convenient and perhaps enjoyable to just go on the gf server.
They wouldn't have to pray if people would play it actively. Nobody has to pray on Native and it's not because there wasn't any other choice. Servers like IG_Battlegrounds were pretty alive before MM came but people switched over to MM instead. Ofc you would have to tryhard it's not exactly a place to fuck around.
Well my point is that a lot of people think: "why go through WBMM when I can just quickly join the GF server".
My point in relation to native is that if you just wanna play NW, the experience of WBMM is similar enough to GF server to the extent where the convenience of GF server makes it the preferred option. However, if you go on native, the experience on something like a deathmatch server or battle server is not even remotely comparable to that of Native Matchmaking. There are no people picking proper classes on proper maps with proper tactics on those deathmatch servers, there's no teamwork and the playerbase is completely different.
Such a difference between the experience of groupfighting and WBMM does not exist on NW. On both, you line up, stab people, repeat. There are no different classes, maps, tactics that can change the experience enough to make WBMM stand out and the playerbase is more or less the same. Therefore convenience is the deciding factor, which means the GF server takes preference for many.
Edit: the only novelty that WBMM offered was a ranking system, which was fun until that novelty wore off. I'm not trying to shittalk your creation btw. WBMM was great for how long it lasted. I'm just trying to explain why it died.