Southern is part of a larger franchise, Govia Thameslink Railway who operate the Southern, Thameslink, Gatwick Express and Great Northern brands. Note the word brand.

GTR are franchised to operate this super large franchise until July 2021 and as part of that, introduce the new Thameslink service through London Bridge as well as maintaining the current service.

The old Southern was merged into this super company last year and have been trying to find ways to save money, the first being closing ticket offices at some of their managed stations such as Peckham Rye, which was rejected. The next has been the reason why they've striked which is to reduce the role of the conductor.