Fuel senders are almost always floats of some kind, either swinging in an arc, or linear, vertically.
If the sender is positioned at the front of the tank, and you're parked with the nose uphill, there can still be sufficient fuel at the pickup to run, but the sender will be at the bottom of its travel and read "empty"...which in the case of your truck's internal logic, inhibits starter function (which is probably a good idea if your truck has that annoying stop/start function, as those starters are insanely expensive compared to their dinosaur ancestors, and prolonged cranking is hard on any of 'em).
Anyway, most vehicles have the senders and pickups roughly at the center of the tank, so you've got a about a 50/50 chance of picking up fuel however the vehicle is oriented.
But I gotta tell ya...and it's going to p--- you off...these days, don't assume there's any well thought-out "reason" for doing anything.
Almost daily, we see things that defy logic from a functional engineering standpoint, and we have a great time poking fun at folks mousing around on their little CAD screens who have very obviously never seen how anything works in the physical world.