The U.S. economy entered 2015 on the most robust streak of consumer spending in years, yet when the first growth figures for 2014 came out Friday they underscored the lack of vigor in the current expansion.

Gross domestic product, the broadest measure of goods and services produced across the U.S., notched an annual growth rate of 2.4% for 2014, the government said Friday, just a touch better than the sluggish average of the nearly six-year-old recovery—and far from the 4% growth of the late 1990s. Fourth-quarter GDP was...