Betty Girl,
Many non legacy UK airlines do day return trips to places like Tenerife, Egypt, Cyprus and Israel that involve over 8-9 hours flying plus the turnround. I don't see this as being much different to a one way to Kenya. At least in Nairobi you get a nice hotel and a beer by the pool with the crew rather than home to the kids to do it all again the next day.
The guys and girls we have work very hard and are constantly in the cabin doing services as they need to hit their selling targets to supplement their low basic wage.
This is the reality with many carriers.
Regards