Why low uptake?
Because Deathmatch is too difficult for novice players, CTF was full of aimbots and there was no cheat protection or way to ban antisocial or lame players, leaving War as the only way to get the game established.
War failed because all the maps are chokepoints - so if there are players that are too good for you, in ut2004, you could go to another bit of the map. In ut3, you will get fragged over and over, for this round, and the next map, and the next map after that since the teams are not balanced or randomised either.
In a nutshell, Epic thought they knew best, ignored everything that the commnity had done to improve ut2004 (team balancing, very big ONS maps, team randomisation) and dumbed it down. They thought their niche was people who want in your face gore.
The actual ut2004 players were fans of an an in depth, intelligent, high learning curve difficult game that takes a lot of practice and mastery.
They made the same difficult high learning curve game but with no tutorial, and gave it an in your face, gansta front end. It is that essential incongruity that broke the game, and all the sub decisions that derived from that initial and wrong creative direction.