Because Bron is the Ironman, him and kobe are two of the current generation players who would make deep playoff runs every year as the number one option
A lot of other superstars bodies would wear out, dwade would never lead his team to 6 finals apperances, his knees were too bad. Durant is too skinny and he had injuries like foot problems, Curry would neither, he is defending his title and muthafukkas in the media already coming up with "70%" excuses.
Maybe Westbrook could take that much every season but I also doubt. Only Kobe and Bron could play on such a high level for that long. Even Duncan had to sit back and sacrifice his stats to win more.