At the time the medieval warm period had led to a slight population increase in Norway. This led to a lack of land in Norway and thus people willing to look to other places to have their own farms.

When Norway was unified under one King, a degree of central rule started to arise, and the Norwegian Kings tried to gain more land for the King to increase the power of the central state/King at the expense of some of the great men. This led to conflicts, revolts, general chafing and thus great men with all their family, allies, hird and thralls to be willing to emigrate.

Iceland may not have been a paradise, but there was plenty of grazing for sheep and cattle, decent fishing, plenty of land (even if most of it was marginal for agriculture) and lots of wild fowl to collect eggs from.

You are probably mixing different times together. In the settlement period Iceland was warmer and conditions better than for example in the 15th or the 18th century. Barley could be grown, and cattle and might not have needed to be housed over the winters (winters are actually fairly mild in Iceland).

Before Iceland was fully populated there might have been valuable resources there, such as Walrus, Cod, seals etc.

The settlement of Iceland happens in an era in which the Norse are generally expanding into variety of directions. Their migrating to the Faroe Isles, to the Britain and the British Isles, they also establishing themselfes in Normandy and they are also settling in Ukraine and establishing Kiev. It is also telling that after Iceland is fully settled they move on to settle Greenland.

Iceland does not appear to be significantly poorer than other norse areas from the settlement and into the 14th century. There was plenty of foreign trade, and writing of the Sagas suggests sources of wealth.