BulowThat's a fair comment, but I don't think it really works for Team Fortress 2. What is TFTV trying to 'sell' here? That 6v6 is a significant and prestigious esport?
In my opinion the idea is probably more to do with the view of the future.
If TF2 ever does get to an e-sport level, even a small one, that will be on the back of 6v6 or whatever similar mode Valve creates with MM. Highlander has been a popular format for people to play, but has never been a popular one for fans or viewers or really had any top level engagement. As well as the pure nightmare of 9 players per team being an esport logistically, there has never been any evidence that HL has a 'fan-base' rather than just players. And an e-sport that justifies content like this requires a fan-base, high level competition, LANs, and obviously requires viewers etc.
For a site that is really driving competitive TF2 forward, imo it makes perfect sense to choose the gamemode that appears to have the most potential (especially with MM being 6v6) and attempt to legitimise that. Dropping Highlander, lower level 6s, 4s, A:R, and any other game-mode allows the site to focus on the one mode with the most potential and also means that new viewers, players, fans etc don't get split up and therefore minimised.