Five years of seniority does lots for career advancement. Guys do not typically take an AGR tour to build flight time. They HAVE the job at the major. They are serving their country, while at the same time improving their military retirement as well as their status with the airline when they return from leave.
As far as a Technician: You actually do get a pension after 5 years of federal civil service (you begin to collect it at age 62.) I would think that people would take a leave from an airline job for a Tech job: in order to have a period of better pay, schedule, and be home more, as compared to being a low seniority airline pilot.
hope I answered your question.