American Passport Holders increase from 3% to 38% since 1989

According to this chart from DadaVis,  the number of American Passport holders has seen a tremendous increase since 1989.   The number has gone from 3% of the population to over 38% of the population.   Does this have to do with the face that passports are now required at the Canadian and Mexican borders?   Does it have to do with the exponential growth of the Cruise industry and/or Caribbean vacations?   Or is this a sign of the rats starting to leave the sinking ship?  Curious.