If I had to guess, it’s a trick to get people engaged.

There’s no link or request for money, so people probably respond more often.

I imagine like many areas of persuasion (like interrogation), getting someone to start talking is the “foot in the door” that starts to snow ball, even if it’s not about anything relevant.

Laying the groundwork to beat a spam filter, probably. If a series of emails are read and not deleted, that does not seem like spam.

It's called "IP warming". When you send bulk emails, there are throttling limits and other things meant to decrease the ability of scammers. So to warm the IP up you have to send on it for awhile. These sorts of blank emails aren't the best way to do it, it's sloppy. But that's the goal.