It seems to me that having multiple vials in the same orientation is redundant, but many levels seems to include this feature. What am I missing? There has to be some reason.
For a spirit level to work the tube cannot be perfectly straight and of constant diameter. For the bubble to float towards the middle either the tube curves up towards the middle (a "block vial") or it has greater diameter towards the middle (a "barrel vial"). If it is curved up towards the middle - the cheapest alternative - it won't work upside down. In levels such as your picture the tubes at either end curve in opposite directions, so that the upper one works.
Contractor-grade levels are expensive, compared to home-grade levels.
Whether that premium cost is justified by build quality or not is a separate topic.
So one way to distinguish the more-expensive ones is to have more visible features/accessories like multiple sight vials.
A lesser second advantage is redundancy - a finely made level becomes nothing more than a fat straight-edge if its vials are broken or become inaccurate. With multiple, you can keep working and continue to use the tool, rather than halting work (which means progress and income stops)
The best tools are those that keep working, so you can keep working.