The mechanic
Uncertainty about a scheduled announcement is priced into options beforehand. Once the announcement resolves the uncertainty, that component of the price disappears regardless of direction. Selling before and buying back after harvests it.
Why the easy money is gone
The pattern is entirely public and mechanically tradeable, so it is priced. The remaining premium is roughly fair compensation for the risk of the move that exceeds what was priced — which happens often enough to matter.
Where an edge might still be
Not in the pattern but in selection: which names systematically over-price their earnings move, and at what size the position stops being survivable. That is a data problem and a sizing problem, and both are automatable — but the edge is thin and requires many uncorrelated instances rather than a few large bets.