Maybe because pilots are reluctant to recruit friends given management's lack of integrity with regards to:

• Critical pay
• Reserve grid manipulation
• Commuter hotels to be paid for "immediately" back in May
• Advertising new-hire flows at six years, when 12 is likely a best case scenario given current numbers
• Reliance on extending lineholders to avoid junior manning
• Offering retention bonuses only to a portion of the pilot group
• One year to even acknowledge a problem with SAP, and another 7 months to initiate a marginally-effective solution
• being serious about growing the airline to they level they've said they would

The problem is management operates with the mentality of "morality is subordinate to expense reduction." Because integrity is a short-term obstacle in achieving the goals of management, they have a belief that everyone working for PSA lacks integrity.

Thus the need to advertise $5k referral bonuses to try to get employees to coerce friends to come to PSA.

Fixing problems would likely be more effective in motivating employees to recruit, but management has apparently calculated that would cost more than $5k per new pilot. So here we are, advertising a bribe on Facebook to try to get employees to tell people PSA is the place to be.