Are there other males in the prides? Potentially could it be a breeding management decision? Rather than castrate/vasectomise the males or implant all the females just simply remove the males from the pride?
Males in Longleat are as follows(I could be wrong though) :
Pride A
Harry: lives with 7 females in one pride
Pride B
Simba
Klaus
Castrated males:
Sylvester
George
Jumba
Toby
Dandy
Ghost
However of the 6 castrated males above I believe one has died in the last 2/3 years but no confirmation of who