Buy the rumor, sell the news.

It gets dumped because people rush to buy when good news is announced, whales dump into the buying to sell for the most amount of profit. Instead of dumping and loosing profits due to the low amount of buy orders at higher prices they sell after new releases. Now Tuesday is the next announcement, so prices should bounce back up and drop somewhat on Tuesday depending on how big the news is on Tuesday. Tuesday's news might be better than expected and price jumps instead of dropping. You might want to search about fundamental analysis and trader psychology.