Well aren't you a ball of sunshine. Clearly they're just doing it because they were really really bored and had nothing better to do.
'Tomorrow, July 7, we’re going to test launching Legion with the Legion Beta, and we’d appreciate your help.
At about 11:00 a.m. PDT on July 7, we’ll take the Beta down for a few hours to prepare. Then, at 3:00 p.m. PDT, we’ll bring the Beta up for testers to log in. During this time, you will only have access to Warlords of Draenor content, and any of your characters above level 100 will temporarily be unable to login. Once enough players have logged in, we will begin broadcasting server messages to indicate that Legion is about to go “live”.
As the expansion “launches”, you will be automatically prompted with new quests to start your adventures in Legion. Please follow them through to conclusion, and play through your class Order Hall opening quests. This will give us a useful look at our live launch.
We need your help identifying issues, and we’ll be looking for your feedback on the test launch in this thread and via in-game bug reports.
Thank you very much!'
Bolded the important part. Testing to emulate live launch and to see what issues popped up.