It's all about building relationships. In order to make any deal happen, two General Managers and their front offices, have to find some common ground and work together to get a deal done. Some GM's like dealing with certain GM's more than others and that's why you will sometimes see several deals between the same two teams.
For the Toronto Blue Jays and GM Ross Atkins, the last two years have been busy on the trade front. From being a seller at last years deadline, to making trades to improve the team this past offseason, Atkins has grabbed talent from a myriad of clubs around the league.