Because Performance can't be described in words as well as statistics tend to do.
Words or Opinions like him being slow paced, indecisive, inconsistent, poor decision making, lacklustre can't be defined in believable parameters which cannot be disputed as Statistics do.
You can list his goal tally, his assist & there is no denying those but what about Performance, how do i provide you with undisputed parameters of performance?
Hence players should always be judged by their on field performance. Those who actually saw the matches.
Statistics wise Maradona, Pelle had not much to other greats of that era but people who watched them play add to their legacy because Performance is best described by those who saw it.
Ronaldo matches Messi in terms of stats but everyone who watches Messi knows he whips the floor in terms of on pitch application.