There were only 12 teams left in the Negro League when he had 3 of his four great-hitting seasons... after baseball started integrating, taking the top talent out of the league.
Can you name one other scout in the HoF who is there for his scouting?
"First black coach" is the only credit you list that seems close to HOF-worthy consideration. Look at others who are on the outside, looking in:
Joe Torre (.297, 252 HR, 1185 RBI, NL MVP, 2-time AL Mgr of the Year, 5 seasons over .300, including a .363),
Keith Hernandez (.296, 1071 RBI, 5-time All-Star, NL MVP, 8 seasons over .300 including a .344),
Allen Trammell (.285, 1003 RBI, 6-time All-Star, World Series MVP, 5 seasons over .300 including a .343),
Minnie Minoso (.298, 1023 RBI, 7-time All-Star, 8 seasons over .300, and also from the Negro Leagues),
Albert Belle (.295, 381 HR, 1289 RBI, 5-time All-Star, MLB Player of the Year, 4 seasons over .300 including a .357),
Dale Murphy (.265, 398 HR, 1266 RBI, 7-time All-Star, 2-time NL MVP, 4 seasons over .295),
Andre Dawson (.279, 438 HR, 1591 RBI, 8-time All-Star, Rookie of the Year, NL MVP, 6 seasons over .299),
and Jim Rice (.298, 348 HR, 1451 RBI, 8 time All-Star, MLB MVP once, 7 seasons over .300)
(not to mention Pete Rose, of course).
You think Buck O'Neil's lower stats against lesser talent makes him worthy of the honor, when the above have been rejected? Once again, is the Hall of Fame for the best of the best, or is it for politically correct feel-good stories?
Buck O'Neil helped change the game, you have to evaluate him for ALL his contributions, not just cherry pick and make arguements singularly. Saying "Can you name one other scout in the HoF who is there for his scouting?" is just poor logic, as no one is saying he should get in for his scouting alone. And there are literally dozens of HOFers that were elected for their contributions other than playing. Buck should be elected for this contributions as a player, scout, manager and executive.
How did Albert Belle change the game?
As for some of the others excluded, how did Robin Yount, a career .285 hitter that broke .320 only once, get in ahead of them? When you come up with the right answer to that question, you'll understand why Buck O'Neil deserves to be in the Hall.
Already people have forgotten who Albert Belle is, but for anyone that knows baseball, Buck O'Neil is still a major player. That's why he spoke at the last induction Ceremony. Consider how utterly ridiculous it would have been to see Keith Hernandez or Albert Belle speaking at a HOF ceremony.
Tell you what, name ONE person in the HOF that matches or suprasses Buck's contributions in EVERY category that he has contributed to: player, manager, scout, executive.
When you do that, I'll cede the point.