Why Childe? Coz he's limited.
I don't know why Mihoyo insist on only giving limited characters the stage but that's how it is since beginning, sadly. Keqing banner was an anomaly. Looks like she was only getting a rate up just to buy time for Hu Tao, nothing more. At this point, I don't want to get my hopes up for another standard character rate up coz we're, indeed, back to the usual 3 weeks limited banner routine.
The dream is dead.
They may have used her to test how a banner featuring a permanent character would have work.
And it seems like Keching banner was the lowest grossing banner so far, as it was expected.
If you looked at the results of the survey posted a couple of pages before, you'll see a sizeable chunk of the non-F2P playerbase buys either the Welkin Pass, the Battle Pass, or both. Maybe 20 to 50€ in a couple of moments.
The huge spikes that have happened after the release of certain 5* characters aren't caused by F2P people or small spenders, but whales. And chances are you already have all permanent 5* characters if you've spent that much money.
If characters like Keching, Mona or Diluc had had their banner in the first couple of months after the game launched, they'd have probably made quite a lot of money. They didn't, so each passing month reduces the perceived value of those characters further and further.
While we all want more permanent content, this is a gacha game. Limited events create FOMO.
Wish more games took the same approach as Another Eden, where all events are permanent.