First of all, no one knows for sure. But here are a few reasons. many miners sell most of the block reward to recoup the cost of mining, for bitcoin's price to remain constant, these new BTC have to be absorbed 'bought' by market participants. And Not sure that the price of bitcoin actually dropped now.
I sometimes get confused why people, especially those having advanced membership kept on asking this "future stereotype questions." I mean they already know that bitcoin is remarkable in the sense that it has a very unpredictable nature. It's volatile in value and can go up or down, any moment of any moment. Therefore, when it will fall down or if it will continue to improve can only be assumed based on passed market trends, but knowing that information with certainty can't be determined by everyone, even the best and seasoned crypto users.