There's never a satisfactory explanation to my mind as to why they can't employ a new farm manager, to work in parallel with Mr Tranter until he retires, and then take over.
To go for a Doylian explanation (I too had to run and find out) Maybe AF was already thinking of the plot for EOT and Lois Sanger wasn't going to be able to do her thing if Rowan was there being games captain.