Top-scorer awards count every goal equally, and that includes penalties. Because penalty duty is assigned by a coach rather than earned in the box, the award is partly decided before a season begins.
The taker receives a guaranteed supply
A team wins a certain number of penalties across a season through the ordinary course of attacking play, and one player converts nearly all of them.
Those chances arrive without the taker having to create anything, and they convert at a far higher rate than any other situation in football.
A forward who is not his team's taker starts the race several goals behind a rival of identical ability who is.
Some teams simply win more penalties
Sides that attack constantly, carry the ball into the area and draw defenders into tackles are awarded more spot kicks than sides that do not.
So the advantage compounds: the taker at a dominant club receives both more penalties and more open-play chances than the taker at a mid-table one.
The award ends up reflecting team strength through two separate channels at once.
The designation can change mid-season
Penalty duty moves when a taker misses at a decisive moment, when a new signing arrives, or when a coach changes.
A forward who loses the role in the winter can see his scoring rate drop sharply without anything about his play having altered.
These handovers are rarely announced, so the change appears in the standings before anyone explains it.
Awards have not separated the categories
Nearly every top-scorer award counts penalties, and no major one publishes a parallel non-penalty version as the headline figure.
The justification is simplicity: a goal is a goal, and adding categories would complicate an award whose appeal is that it is easy to understand.
Analysts publish the separated figures anyway, and the two lists frequently disagree about who had the better season.
What the distortion does to reputations
A forward who wins a race largely through spot kicks acquires a record that outlives the context in which it was set.
Years later the total is quoted without the breakdown, and the comparison with a rival who took none is made as though the conditions were equal.
Reading historical top-scorer lists therefore requires knowing who took penalties, which is information the lists themselves never carry.