Why don't tags and socks have made in labels on them?

I’m off to a wedding and I’m wearing clothes I don’t normally wear.

Dress shirt — Made in Sri Lanka (never been there)
Pants — Made in Vietnam (never been there)
Socks — ?
Tie — ?
Boxers — Probably Nicaragua or Thailand (the tag has worn off)

Anyhow, this got me thinking: Why is it that some items of clothing don’t have a Made in Label on them? I know that the packaging they came in was probably labeled, but still.