Why do businesses help pay the student loans of their employees?

It seems like they could just pay a higher salary or whatever salary it takes to attract the kind of workers they want. If applicants with student loans want higher salaries and that's what it takes to get them, then why not just do that? Instead of paying, say $5,000 of their loans each year, why not just offer a salary of $5,000 more each year?

It may have to do with signalling. Here is Wikipedia says about it:

"In contract theory, signalling (or signaling; see spelling differences) is the idea that one party (termed the agent) credibly conveys some information about itself to another party (the principal). For example, in Michael Spence's job-market signalling model, (potential) employees send a signal about their ability level to the employer by acquiring education credentials. The informational value of the credential comes from the fact that the employer believes the credential is positively correlated with having greater ability and difficult for low ability employees to obtain. Thus the credential enables the employer to reliably distinguish low ability workers from high ability workers." 

See These Companies Are Helping Workers Pay Down Student Loans: More professionals want employers to help with loans; ‘It has been a powerful retention tool’ by Lindsay Ellis of The Wall Street Journal. Excerpts:

"Even a few hundred dollars a year directed toward loan repayment can generate goodwill, said Uri Gneezy, a University of California, San Diego, economist and the author of a recent book about how incentives work and motivate people. 

Such directed payments can mean more to employees than a raise, he said. 

Designating specific funds to help defray a person’s student-loan payment signals that the employer is grateful for the worker’s education and recognizes the financial toll it took to prepare for the role, Dr. Gneezy said."

Related post:

More employers offer workers help paying off student loans (2019)

Why do employers pay extra money to people who study a bunch of subjects in college that they don’t actually need you to know? Signaling (2018)