Why did the hotel manager refuse to seeing Charley Thomas a hotel room?

The hotel manager refused to assign Charley Thomas a hotel room because he had dark skin. This was during 1910, when the team he was in was going on a trip for a ball game. Branch Rickey, the coach, threatened to leave the hotel if they weren't going to accept him. He was lying because he knew other hotels were also going to refuse "dark-skinned" to a room. Soon, he suggested for a cot to be placed in his room for Charley to sleep in.