Playing for the "Heat" is exhausting mentally and physically. The training standards are the most exacting in the Association. The physical and mental effort demanded in playing defense is depleting. Pat Riley does not recognize mental fatigue, he didn't after the 2010 Finals when player after player told him in their exit interviews. That was the last season of the "Heatles."
The "Heat" played in the NBA Finals in 2020. Because of COVID-19 their season didn't end until October 11. They played their first game of the current 2020/21 season on December 23. Two and one-half months between games. Not including training and pre-season activities. Anybody watching the "Heat" in the bubble in the playoffs saw the laser focus of the entire squad. Nothing else existed for them but life in the bubble. You cannot replicate nor sustain that mental dilation traveling from city to city, and over seventy-two games. It is not humanly reasonable to expect it.
There are only sixteen games left in the 2020/21 season. Miami is 28-28, in seventh place. "You are what your record says you are," Erik Spoelstra has said many times over the years. .500 is what they are and what they will be at season's end.