The Railway Labor Act (RLA) makes working for an airline (or railroad) significantly different than working in other industries as the federal rules governing your employment are quite different.
The RLA was originally designed to prevent strikes or lock-outs which would disrupt the country's transportation system. First railroads, then later airlines. The RLA prohibits covered labor groups from striking, and employers from locking-out covered labor groups, without first proceeding through a complex process which involves the National Mediation Board (NMB). Both labor and employers are required to maintain Status Quo during the process so employer's can not change work rules outside of the process.
The goal is to avoid disruptions in the transportation system and, for the most part, it does that. It also produces situations that don't make a lot of sense when viewed from the outside without any context or understanding of the RLA.
Many Frontier pilots are leaving and many more are trying to leave. The worse it gets, the more who will leave.