Yamcha first described the Kamehameha as a technique that concentrates one’s “latent power” into one point before firing, and the Daizenshuus get behind this explanation. It follows that most Ki attacks probably follow the same logic, drawing from inner sources that fighters probably don’t have access to.
The attacks must be constantly upgraded (If not replaced: See how Vegeta never used the same attack twice until Super) to keep up with the new heights the power of the Z Fighter uses. Otherwise the attacks either ends up not drawing all the power needed (e.g. Cell’s Kamehameha, which probably had a potency below what his power level would dictate, possibly even as low as Goku’s Kamehameha on Raditz based on Piccolo’s comparison) or needing a drawn out charging time to reach it’s full power (Piccolo’s then brand new Makkankosappo on the Raditz fight).