I assumed it was the amount of power used. Wenwu was using them in small fights and to extend his life, Shang-Chi used them to destroy an interdimensional monster.
Overall, I thought the movie was good not great. Maybe I'm just getting burned out on Marvel movies, but I didn't really think it was anything new or innovative. Simu Liu and Tony Lueng were great, and, while I'm not her biggest fan, Awkwafina did well.
Anyone else notice the Widow fighting someone with Extremis in the fight club?