Because people watched him play and felt it was that great?
I don't have him near top 5 but this idea fans have today that you need to rank every top whatever number of all-time players based on basketball reference resumes is about.
Most of his best games are on YouTube. It's not like he was in the 1950s and you need someone in their 70s to explain it. Watching someone play > reading stats and accolades
It's almost like the ideas for change always benefit the team in the flair of poster. What a random coincidence that happens 99% of the time!