It's probably no surprise that the disappointment over the last two years has coincided with the two most populous Yankee teams in franchise history. In 2013 the team used a franchise record 56 different players throughout the course of the season which was five more than the previous record. Last year they broke that record by using a whopping 58 players to fill out the roster. As injuries and ineffectiveness piled up the Yankees scrambled to find replacements but the results weren't always pretty. Outside of a couple savvy trades the replacements usually came in the form of a minor leaguer from an underwhelming Yankee system.
To highlight the negative impact of using all those players on team performance, the graph below plots Yankee win totals against the number of players used for each season since 1996. That year was used as the cutoff because the strike shortened 1994 and 1995 seasons would have skewed the trend and going back to years prior to that would take us into an era where disabled list stints were fewer and playing through pain and injury was the norm. (Data courtesy of Baseball Reference)
The aforementioned 2013 and 2014 teams are represented by those two plot points at the bottom right of the graph. On the flip side, that little guy at the top left represents the infamous 1998 Yankees. While the sample size here is small and things such as the quality of players aren't taken into account, it's clear that the more players the Yankees use, the worse they perform on the field. So the key to a successful 2015 campaign could be as simple as avoiding the injury bug and keeping players off the disabled list.
That will be easier said than done. Each Yankee penciled into the starting lineup for 2015, with the exception of the recently acquired Didi Gregorius, is on the wrong side of 30 and most of them have struggled with injuries in the past. With the odds stacked against them it will require a considerable amount of luck for the Yankees, but a healthy team will most likely mean happy fans this year.