You would think, but management can often have difficulty seeing how macro trends affect them. From their perspective, they shouldn't have to pay more for the same and adding new staff at higher pay than old staff seems unfair.

My previous job had difficulty finding talented engineers, party due to comparatively low salary offers. When I and two others left our team of 8 and two more made it known they were actively looking because we saw all trends outside our office, it became clearer to management. Only when 3/8ths of their staff left did they make major changes to their existing packages. And even then, pay is significantly below market. (Though they have the best time off and fringe benefits in town.)