Penalty run-ups have shortened considerably over the last few decades. The change follows from a shift in what a penalty taker is trying to achieve, which is placement rather than power.
Long approaches were built for power
A run-up of several strides generates momentum that can be transferred into the strike, producing a shot that beats a goalkeeper by speed alone.
Against keepers who committed early to a side, power was a reasonable strategy, since the ball simply had to arrive before the dive completed.
The cost was control: a fast approach makes precise placement harder, and misses from long run-ups tend to be high rather than saved.
Placement became the priority
A penalty struck accurately into a corner at moderate pace cannot be reached even by a keeper who guesses correctly.
Achieving that accuracy requires a stable body position at contact, which a short, controlled approach delivers far more reliably.
Takers accordingly traded speed for balance, and the modern run-up is often three or four measured steps taken at walking pace.
Reading the keeper requires a slower approach
Many takers now decide their side during the approach rather than beforehand, watching for the keeper's first movement.
That decision needs time, and a sprinting approach removes it, because the strike arrives before the information does.
A short run-up allows the taker to keep his head up until the final stride, which is when the keeper's weight shift becomes visible.
Rule changes closed off the alternatives
Stopping completely during the run-up, or feinting after completing it, is an offence, which limits how much a long approach can be used to deceive.
Officials enforce this consistently, and the punishment is severe enough that few takers risk it in a decisive kick.
The elaborate stuttering approaches that once produced hesitation therefore lost much of their value, and the technique has narrowed as a result.
What the shorter run-up costs
Reduced power means a poorly placed penalty is now savable rather than simply too fast to reach, so the margin for error is smaller.
It also gives the goalkeeper a longer view of the taker's body, since there is less speed disguising the shape of the strike.
The approach that has survived is a compromise: short enough to control, long enough to strike firmly, and slow enough to see what the keeper does.