[Man-of-the-Wold]

Well, arguably the Master of Esgorath was elected, even if by perhaps an elite electorate.

But Legolas was a prince, technically, but perhaps he had an older brother, who was the true heir, but given Elvish immortality this might have been of relatively little matter.

In the First Age one hears talk of the princes of the Noldor, but among the Sindar there is little of that. Cirdan is well, just Cirdan and so forth. And the Noldorin realms were much more majestic and regal.

I think for a place like Thranduil's realm, and especially by that time in the history of the Elves, they had sort of let go of such formality and so forth, and it wasn't really appropriate any more.

Also, Odopher and Thranduil were sort of selected rulers of the East Elves, just as Celeborn and Galadriel were after the passing of Amroth, and Celeborn and Galadriel were not consistently entitled as King and Queen, but rather as Lord and Lady. Had Thranduil died it may not have been automatic that he was succeeded by a son. Some other arrangement may have been better, for that realm, remember in that the Green-Elves of Ossiriand didn't have a King after the death of Denethor, but took Beren and Dior for time as their ruler.

In a sense, for that time and place, it was simply pretentious and unnecessary for Legolas to carry the title of "prince".