Everyone is not buying and selling during these times because of the nature of the game. For example, half the teams in each league make the playoffs. If I am making a playoff run, I am not going to be selling my core players that I need to make a playoff run nor will I be buying players during the playoffs. So this means demand will be high for players at the end of the season, while supply is low and during the playoffs demand will be low since not all teams will be looking to buy players.