Don’t get me wrong, you CAN use Nostr DMs obviously. They’re just not robust or reliable in their current form. No amount of wanting them to be is going to change that. Most people have other messaging apps, so find something they have and use that. It’s not like I can say what people already have. I have half a dozen apps for messaging various people, depending what they use. It’s just the state of things. The best you could probably do with Nostr is to run your own relay and only allow people you DM with on Nostr to connect to it so it preserves those messages.