“The colonists didn’t.”
Who owned, bought and sold other human beings to be slaves in the American Colonies?
Few, if any, American ships/captains were directly involved in obtaining African slaves.
And colonial ships or vendors didn't even exist. (The sponsoring companies might have been involved but their main interest was in taking wealth OUT of the colonies, not buying property to bring into them).
See reference to Rhode Island in the original article regarding indentured European workers' 10 year servitude being applied to African slaves as well.
Like it or not, I'd venture that about half of the Mayflower & associated descendants' ancestors came over under indenture (contract) or threat of prison.
(In tracing our lineage, my mother turned up the ship her esteemed ancestor rode to the new world, the manifest read "Irish labor"...just prior to independence)