Well, because in the fiction, the Walkers have to be bedraggled, forlorn tramps, alone in the world, thrown out on the roadside by an ungracious ‘friend’ who is tired of her ‘squatters’, having grudgingly given them houseroom (well, at least a floor) for weeks longer than planned, because Moth apparently needs to recover from whatever it is the Angel Session in Glastonbury did to him, and is grudgingly letting them leave their van on her drive. In this version of events, Jan just wants them gone, and slings them out on the roadside like someone abandoning an unwanted pet.
However, if ‘Jan’ is really a hospitable, well-disposed sibling who says ‘Stay as long as you like!’ or drives them to within a foot of the SWCP start and waves them off with a packed lunch and reminders about sunscreen and Moth’s drugs, shouting ‘Have a lovely holiday!’, and tells them to phone her day or night if they need collecting — that’s a whole different story and far less liable to pluck at the heart strings.
It’s more Ramblers’ Association or Duke of Edinburgh trek than Desperate Walk to Redemption.
(Obviously she’s not going to beg SW not to drag a dying man on a challenging 630- mile trek, because he isn’t dying, and they’re just off for a nice little holiday.)
And of course if we think of ‘Anne’ on the podcast remembering that the Walkers went on at least two walking holidays while staying on her farm, once using TW’s PIP and once using the fleece-wrapping money, it seems likely that their first stint on the path came out of a period of leisure and voluntary unemployment, while lying low from debt collectors and living rent-free at Anne’s farm, where they were no longer bothering even to pretend to declare bankruptcy, find work, or help out on the farm. Two grifters escaping the obligation of helping a family member in need, rather than two desperate homeless people.