Top-scorer races are usually discussed as contests of finishing form. They are more often decided by who stayed fit, because absence removes chances that no subsequent improvement can recover.
Missed matches are unrecoverable
A forward who misses six weeks loses the chances that would have arrived in those matches, and those chances do not reappear later in the season.
Even an outstanding run on his return only restores his rate, not the volume, so the deficit persists to the final day.
A rival scoring at a modest rate but playing every match will frequently finish ahead of a far better finisher who missed two months.
When the injury falls matters as much as its length
An absence early in a season leaves time to recover the gap, because there are enough remaining matches for a high rate to accumulate.
The same absence in the closing months is decisive, since the remaining fixtures cannot supply the required volume of chances.
This is why a race can appear settled in the spring despite the leading scorer having been comfortably outperformed for the year as a whole.
Returning is not the same as being available
A forward coming back from a significant injury is typically eased in through substitute appearances before he starts again.
Those weeks produce very few goals, so the effective absence is longer than the period he spent unavailable for selection.
Sharpness in front of goal also takes time to return, because timing runs against a defensive line is a rhythm that decays without matches.
Rotation acts as a milder version of the same thing
A striker at a club competing on several fronts may be rested regularly, losing league minutes to preserve him for other competitions.
His rival at a club with only domestic commitments plays continuously and accumulates chances the rested player never sees.
The award therefore favours forwards whose clubs have fewer fixtures, which is close to the opposite of what people assume it measures.
Why availability is treated as luck
Injuries are partly random, but the ability to complete a season is also a genuine attribute involving physical robustness and load management.
Forwards with long records of playing almost every match are demonstrating something real, even if it is not the skill the award is named for.
Discounting it entirely misreads the competition, since a top-scorer race is as much an endurance event as a finishing one.