A top-scorer race still level on the final day changes how a match is played. Teams whose league position is already settled behave in ways that would be indefensible in any other week.
Penalty duty gets reassigned openly
A team with nothing at stake will frequently hand a spot kick to its leading scorer regardless of who normally takes them.
Nobody pretends otherwise, and the gesture is generally treated as a courtesy rather than as a distortion of the competition.
The effect on the race is direct, since a single penalty can settle an award contested over an entire season.
Teammates change their own decisions
Players in scoring positions pass to the contender instead of shooting, and the square ball into the six-yard box becomes noticeably more common.
Substitutions are also managed around it, with the scorer kept on regardless of the state of the match.
None of this breaks any rule, and all of it means the final-day goals are produced under conditions unlike the rest of the season.
Opponents face an awkward position
A team with nothing to play for is not obliged to defend seriously, and a team fighting relegation on the same afternoon absolutely is.
So one contender may face a defence with everything at stake while his rival faces one on holiday, which is decided entirely by the fixture list.
Competitions accept this because scheduling every final-day match simultaneously already solves the larger problem of collusion over league positions.
The scorer's own behaviour changes
A forward chasing an award takes shots he would ordinarily pass up, and shoots from positions where a teammate is better placed.
Managers occasionally address this publicly, since a player prioritising a personal total in a match that matters is a genuine problem.
Where the team has nothing to play for, the same behaviour is tolerated and often actively supported by everyone on the pitch.
Why the awards leave it alone
Policing intent is impossible, and any rule attempting to distinguish a genuine penalty decision from a gifted one would be unenforceable.
The alternative of excluding final-day goals is worse, because it would invalidate part of a season for reasons unrelated to the players.
So the incentive remains, and every few seasons it produces an afternoon that decides an award in a manner nobody would have designed.