I can understand having automatic playout overnight, but during the day when channels like Challenge might have a decent amount of viewers, it's lazy. It's nice to think there's somebody somewhere pushing the buttons, in the same way there's a sense of comfort listening to a DJ on a radio rather than leaving your iPod on shuffle.
There will be someone in a transmission suite looking after the channel.... although they might be looking after Challenge and a few others. It might well be that at night the channel is getting more attention as the other ones from the same suite close down
You are confusing 'automatic playout' with unattended playout. Every TV channel has automation playing out their programmes, and that's been the case for about 20 years; but only a few of the very cheapest, little watched channel will have no human intervention at all.
Without automatic playout I doubt there'd be much programming on air after about 2am.
If everything had to be manual and there were 3 or 4 people per channel then they wouldn't be able to afford to broadcast after 2.... but then they wouldn't be able to afford to broadcast the rest of the day either!