One reason this is true is because Elizabeth's reign represented a brief respite between the turmoil caused by the English Reformation initiated by Henry VIII in the sixteenth century and crises that led to the English Civil War in the seventeenth century. While it was unsatisfactory to both Catholics and, later, to the growing Puritan movement, the so-called "Elizabethan Settlement" provided a basis for internal peace that lasted most of her reign, albeit with a number of conspiracies against the queen.
Another reason is that England emerged as a growing European power during this period. It was, of course, under Elizabeth that the English defeated the famous Spanish Armada in 1588. While the victory did not immediately make England into a major naval power, it did help them achieve a major foreign policy goal by averting Spanish victory in the Netherlands. Additionally, England began to tentatively seek colonies in the New World, and squadrons under Sir Francis Drake terrorized Spanish fleets and ports around the world to great effect. These factors, along with the considerable cult of personality surrounding "Good Queen Bess" contributed to a rising sense of pride in the English nation.
Finally, and most memorably, the Elizabethan period represented a recognized high point, or a renaissance, in drama, poetry, and other vernacular literature. Of course, William Shakespeare wrote during the latter years of Elizabeth's reign, but the period was also characterized by such playwrights as Ben Jonson and Christopher Marlowe, as well as poets Edmund Spenser and Walter Raleigh. This flowering of literature, encouraged by Elizabeth herself and largely (especially the poets) associated with court life, is perhaps the reason that the Elizabethan period is often characterized as a "golden age" in English history.