The word for "dear", Kara, is used very often in the Esperanto Duolingo course. Much more often than I would use the expression on English. Why?
Saluton kara! Chuck Smith, the coordinator of the Duolingo course, responded to a similar question in the Facebook group for Duolingo Esperanto Learners:
It's definitely used more in Esperanto than English and we wanted to reflect that in the course. Looks like we succeeded! :)
You can use kara for everyone you feel part of the same group you are. This is why many Esperanto speakers use this word when saluting other Esperanto speakers.