Don't know why they were done and I realize you didn't ask how to repair. Here is a suggestion for you or anyone else,
The least expensive way, "easiest" to fix, is find someone (electrician or HVAC) with a Greenlee type hole punch the same size that was used. Make round patches and weld slowly, one at a time. The indent portion of some patches can be made with round stock as a mandrel. Use a large piece of metal and a rod, indent a long dimple in it, same size and depth as door dimples. Then punch out each. Locate punch on dimple to duplicate each hole patch. Work each patch a little after punching out until good fit. Use this as a brainstorm for your own method as you see fit.
I don't advise a big skin patch from a vendor or donor door unless it's used as punchout material. It is a method some will like. It has a slight warp risk to do that. If you don't have a welder, buy a donor door and transfer all hardware....but that will have it's own can of worms. If you can do the weld repair without removing door, that is way less work than to realign door. Spot welding does not need to lay flat.
A round hole has less impact on structure usually. No worry to leave alone unless oil canning/noise.
A round patch has no stress corners and easier to weld in. looks like only about four need a dimple. One hole will be covered by a panel.
There are various inner cowl panels available that may have the same dimple. They may be a good head start for punchout patches.... or of course, as said, a door skin.
