"And why did Columbus actually leave his crew there upon the island when he sailed back? "
I thought one of the ships was destroyed on the rocks, so he did not have enough transport.
;)
Actually...there was more than enough room on the two other vessels for the crew of the 3rd boat. He left them to help ensure that the Queen would allow him a second trip (she wouldn't dare leave poor Spaniards behind on a desert island).