I am guessing different actors decide on parts for different reasons. Some may be the type who need a different project every so often to get them going some may love the continuity of a long term project. Some may find having movies challenging having to get the character down in a few weeks, while others may like developing a character over a long season. I think doing the same play over and over again could get boring but some actors may like the audience feed back so much it remains a challenge. Same for like NCIS or SUV actors do they find that all that challenging still its not like any of them seem to just be doing it for the money. I mean how much more more does Mark Harmon need? So it probably is still joyful even if it not groundbreaking or a new challenge.
More power to all of them to continue to try to make the most of the opportunities presented to them. Be it is a wide variety of projects in different mediums or a long running gig I hope they get to do what works for them.