Why do some oak trees retain most of their leaves until spring?

Because they can.

The advantage of holding onto dead leaves overwinter is that they will add to the oak's mulch (not another tree's) in the Spring. Thus, the oaks can recoup some of their loss.

The danger of keeping dead leaves on a tree is the formation of icicles that would snap branches of the tree. Oaks are incredibly strong, and can survive the formation of such icicles.

Interestingly, beeches also keep their leaves but only on the lower, stronger branches.