They still translate them to modern Icelandic. Besides there is a lot of difference between the different Eddas as well as the different parts of them. Since they were written from the thirteenth century forward they are also arguably more like Chaucer than Beowulf.

I also think that the Eddas play a very big part in Icelandic national identity. Considering this and the tiny population it might well be a big reason for the slower language shift. Compare this to Barrayar where most of the national identity seems to come from stories and historical happenings during the time of isolation (and later the Cetagandan war) and we don't hear anything of the times before they arrived on Barrayar.