When Starbucks and JPMorgan Chase last month separately revealed plans to raise worker pay, they were the most recent in a steady barrage of high-profile announcements of companies' human resources strategies.

News releases and social media posts trumpeting generous parental leave policies, unlimited vacation time, flexible work arrangements and revamped performance-management systems have become as reliable as earnings statements, reflecting a scramble to retain and attract talent in a tightening labor market.

But while using HR as PR may burnish a company's image — and help the cause for better working conditions generally when competitors jump on board — that public relations push could be causing job malaise among workers at employers without such a loud bullhorn.

"There's a perception that the grass is greener on the other side of the fence," said Brian Kropp, practice leader at business advisory firm CEB.

A recent report from CEB found that workers' discretionary effort — defined as "the willingness to go above and beyond the call of duty, such as helping people with heavy workloads, volunteering for additional duties and looking for ways to perform the job more efficiently" — is at a four-year low. Meanwhile, globally, active job-seeking activity is up.

That's despite findings that confidence in the business environment is at a three-year low, suggesting people think things are bad where they are but better elsewhere.

Kropp said people may hear other companies making a to-do over their excellent benefits and feel miffed that they are missing out. Problem is, he said, if they leave their job for what they think is a cooler company, they often encounter other challenges and are no happier.

Jason Guggisberg, regional vice president of Adecco Staffing USA, said he is seeing a grass-is-greener syndrome among employees, who often are attracted by a workplace's culture. Millennials, his research found, are particularly susceptible, drawn by perceived growth opportunities.

But many soon realize the new company wasn't what they thought it would be.

"They come back to us wanting to go back to their previous role," Guggisberg said. High performers are typically welcomed back by their former employers, he added.

Touting HR policies to draw and keep talent is not a new idea, said Nicholas Pearce, clinical professor of management and organizations at Northwestern University's Kellogg School of Management.

Workplace culture for decades has been a company's most precious competitive advantage, beating strategy because it isn't so easily imitated.

But it also isn't easily shaped, which is one reason why organizations struggle with employee engagement, which in turn is connected to retention and discretionary effort.

Low levels of discretionary effort are a serious problem in an era when companies need their employees to be critical thinkers, problem solvers and brand ambassadors, Pearce said.

"In the knowledge economy, employers need their people to bring their heads, their hands and their hearts to work," he said. "There is no amount of money you can pay someone to make them care, to make them be creative, to bring their best ideas," Pearce said.