They finished the year in 2019 with a rotation of:
Ryu
Buehler
Kershaw
Maeda
Hill
Stripling was swing man of course and they were keeping him at that point
Urias was emerging as a probable front line starter
I guess they felt they didn't want to gamble on Ryu being healthy for 4 years
It always troubled me a little bit that the Dodgers wanted no part of keeping him at a seemingly reasonable 20M AAV at the time
That probably means something. Though it was probably just an unwillingness to commit to 4 years.