WASHINGTON — The U.S. economy has delivered steady if only modest gains for most Americans since the Great Recession ended in 2009. It’s been a frustration for many.

Yet the very sluggishness of the economic expansion helps explain why it’s now the second-longest on record and why more of the country might soon benefit from higher pay.

Nearly nine years into the recovery, the job market keeps delivering: The government said Friday that employers added 164,000 jobs in April — the 91st straight month of hiring growth, the longest such streak on record. More tellingly, the unemployment rate fell to 3.9 percent, the lowest since December 2000. Eight years ago, the jobless rate was 10 percent.

But for much of the expansion, many people have felt left behind. Some have found only part-time work. Pay growth, on average, has been meager. The stock market boom and low interest rates that defined the recovery have favored the wealthy.

The economy’s modest growth, though, has helped prevent it from overheating and skidding into another recession, as often happened during more robust expansions.