Any mapping app is only as good as its data, and the developer's willingness to send you off into the unknown.
If you zoom on that parking lot (or forest preserve) in map view, do you see the actual road/grid/footpath layout, or is it just an expanse of empty space? If it's empty space, should you expect the mapping app to create a path?
I just tried to plan walking and driving routes to the center of a nearby woodland preserve, using both Apple Maps and Google Maps. That preserve is bisected by a dirt road that has been there for nearly 100 years (the street was removed from the maps in the 1970s, following conversion to parkland). I placed the "pin" as close to that road as I could. Had the road's existence been known, the routes would have included it. Neither app presented a viable route.
Apple's walking route was by far shorter, ending on a street to the west of the woodland (I would have had to cut through a private yard to reach the woodland, and find my own path to the destination point). The route included this note: "Directions end at closest road to destination." Google's took me on a much longer route through a strip mall to the east of the woodland (I live to the west of the woodland), and from there, it extrapolated a straight-line path to my chosen point within the park. The route would have taken me over the edge of a 15-foot high retaining wall behind the strip mall.
Apple chose to end the route in the absence of useable data, while Google was willing to go out on a limb.
I tried to get Google to extrapolate a walking route in another park to see if it would take me over a 300-foot cliff. In that case, it refused, plotting a very long but safe route via paved park roads (there are footpaths that would have been shorter, but again, they weren't mapped). Perhaps there's a change-of-elevation threshold that the 15-foot retaining wall didn't trigger?
I'd imagine the legal departments at both Apple and Google get involved in this sort of thing. It's one thing to provide a driving/walking route based on inaccurate data - they can write a disclaimer to cover that sort of thing. It's another to make a recommendation in the absence of data.