Why did the elves willingly go fight morgoth when in one on one combat?

As far as I know, only Fingolfin personally fought Morgoth, and he only did so out of despair after seeing the defeat of his people. As andrewlaubacher stated, Morgoth was no longer at the peak of his power, although he was victorious in the duel. The victory came at a high price, however, as he was wounded several times.

The Elves who fought Morgoth in personal combat were quite powerful in their own right and perhaps a bit too confident in their own prowess. Morgoth was not at the height of his power in the First Age as he has placed much of his power into the corruption of Arda.