Just because we don’t see it as often in the saga films doesn’t mean it isn’t a common way of communicating. Think of it like texting. Lando doesn’t have a phone (transmission device), but he can still receive messages through the computer or something. No droid necessary.
If you look at Wookieepedia it basically says the same thing. He is able to receive messages from them, but for whatever reason doesn’t do holographic chats.
He decides to give the trio the information but doesn’t want to get more involved than that. He changes his mind later.
Lando doesn’t do the same method of communication with them because he doesn’t know where to send the “text message” to, if you will.