Odds are they're related to production than anything about the finished product.

For example, anodizing rims requires submersion in baths of various chemicals, Air vent and drain holes are necessary if the rim is anodized after being completed but before drilling, or if the rim has corner channels that are separate from drilled area, as is common on many single wall rims with pinned construction.

Multiple drain holes are often drilled to speed draining, or because a single hole can get air bound and not drain properly.

Edit, I didn't see a clear picture when I posted earlier. Looking again, there's another possibility. Those rims are joined with pins in the channels along the outer edges. So, one purpose for the holes is as a stop for the pin, to ensure that it doesn't get pushed into one side rather than evenly engage both sides. Also, since the pin is blocking the channel added holes are needed for draining if the rim is anodized after being formed.