can someone explain to me why holding a 3x leveraged stock long term is bad and can lead to losses?

i keep hearing that if you hold TQQQ or something similar for a long term hold you will lose money from volatility decay.
so if i bought TQQQ say at $20… and held it for a couple of years and let’s say i sold it 5 years from now when it hit $30… would i not profit off that $10/share?