Read this: Several MLB teams used to play regular exhibition games during the year against nearby teams in the other major league, but regular-season interleague play has made such games unnecessary. The two Canadian MLB teams, the Toronto Blue Jays of the American League and the Montreal Expos of the National League, met annually to play the Pearson Cup exhibition game; this tradition ended when the Expos moved to Washington DC for the 2005 season. Similarly, the New York Yankees played in the Mayor's Trophy Game against various local rivals from 1946 to 1983.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What development has made it unnecessary for MLB teams to play exhibition games with teams from other leagues?
regular-season interleague play