Savage Seven became the Furious Four. The Furious Four is a derivative sub-brand (a branch, or off shoot) from the Brothers In Arms brand. It is a separate story involving separate characters.
In the entertainment industry, you often find branches (or "spin offs") from a popular brand. For example, in America, there's an animated TV show called "Family Guy". A while back, the creators of Family Guy decided to take one of the characters (Cleveland) and make a TV show involving Cleveland and other brand new characters. Just because they started making "The Cleveland Show" doesn't mean they stop making "Family Guy". It just gives them a chance to try something new while still keeping the original (mostly) the same.
Randy and Brian Martel have mentioned several times in interviews before that we're not done with the story of Matt Baker, Joe Hartsock, Corrion and the rest of the guys from the Brothers In Arms series.
Ubisoft and Gearbox just wanted to try something a little bit different for now to see how it goes.