The same reason I fly with a ton of FOs from a particular “flow” regional. They want to move on when given the opportunity and don’t want to wait for their turn at the flow that may or may not happen if something goes wrong and that door slams shut. It doesn’t mean that they can’t still apply to the applicable legacy and get hired outside the flow (especially these days). Flows are not for the benefit of the pilot or to staff the parent legacy. The are for the benefit of the legacy to keep their regional feed staffed. Dangle the carrot so people want to work there. Flows are great for people with major skeletons who have no other shot at a legacy. Otherwise get out to wherever you can, whenever you can and keep a current app with the legacy of that’s your jam.