In the first three seasons, fans watched Mary and Matthew Crawley go from hating each other to falling in love, getting married, and having a baby. However, Matthew and Mary’s happy ending was short-lived. According to Town And Country, actor Dan Stevens, who played Matthew, chose not to renew his contract after the first three seasons. Julian Fellowes told Radio Times, however, that he didn’t know Stevens wouldn’t return until Season 3 was well underway.
That same year, Downton Abbey also lost Jessica Findlay Brown, who played Sybil Crawley. According to Fellowes, Findlay Brown was upfront from the beginning about her intention to stay for just three seasons. After both Stevens and Findlay Brown left, Downton Abbey did find its footing once again. However, when Season 5 ended, two other characters said their goodbyes.
Downton executive producer Gareth Neame told Deadline that the departures of Allen Leech, who played Tom Branson, and Lily James, who played Rose MacClare, left the door open for an eventual return. Still, losing four main characters in just five seasons is a lot for any show so it’s no wonder the showrunners knew it was the right time to close the curtain and cancel the series.