Pick used to be effectively a shop window for the pay TV channels, it used to be called Sky 3 and was initially exclusive to Freeview, before it morphed into what it is now.
To be honest looking at the state of Challenge and the fact it's social media is long abandoned and the website has vanished, it's probably just limping along on life support presumably for some contractual reason or two. It's not the same channel it used to be and I sometimes wonder whether it would be kinder for Sky to either just put it out of its misery or flog it to somebody else - it is a unique channel in the marketplace but its been obvious for a while now they don't know what they want to do with it.
Wasn't Challenge once part of what is now the UKTV family? When it was Flextech?
UKTV is a network with too many channels and not enough content they will show anymore.
Much of the older content is now deemed "inappropriate" for today's audiences, hence is not shown. This is partly why GOLD, for example, has endless repeats of OFAH and LOTSW to fill the schedules.
UK Gold should have remained two channels (UK Gold + Uk Gold 2), with possibly a +1 for each.