I was recently looking for another crate for my records when I found this Vinyl Factory article:

Why it’s Criminal to Store Records in Milkcrates.

That article in turn linked to an article on Modern Farmer.

The Modern Farmer article doesn't go into milk crates for the purpose of vinyl record storage, but it talks about an even bigger market for the plastic within the crates:

The big problem is semi-organized theft for the purpose of grinding them up and selling them,” says Clay Detlefsen, vice-president and counsel for the IDFA...

In 2010, The Wall Street Journal reported on a Baltimore-area crime ring that stole millions of dollars of plastic for resale to recycling companies...

Milk crates are made of petroleum-derived high-density polyethylene, and their price rises and falls with the price of oil

When I stumbled upon the Vinyl Factory article, I worried vinyl records played a large role in this, but it turns out just 5 percent of crate loss to “personal use”.

Both articles have tons of interesting info in them. Hat tip to The Vinyl Factory for the initial article that led me down this rabbit hole.