One thing I haven't seen mentioned is that I see recruiters getting resumes from places like LinkedIn and cold-calling those people, based on experience and keywords in their resumes. And if those people don't need to bother with cover letters, maybe no one really cares.

People might also think that since companies are still crying about the shortage of programmers it's still a "renter's market" and that enough employers are desperate enough to not squabble over missing cover letters.

But I still have no great theory about why people wouldn't have at least a single paragraph about themselves that they paste into emails to make them seem slightly more personal.