The simple reason
Elastic needs recovery time.
When a bra is worn all day, the band and wings stretch with body movement. For fuller-bust shoppers, the band does a lot of support work. Giving a bra a rest day helps it return closer to its original tension before the next wear.
A five-pack makes outfit planning easier.
Different outfits need different finishes. Fabric cups usually work better under smooth T-shirts. Lace cups or lace wings can be a good choice when texture is not an issue. A multi-bra rotation gives you more flexibility without rebuilding your drawer one bra at a time.
How to care for a weekly bra rotation.
Clasp hooks before washing, use a mesh bag, wash cold and air dry. Avoid tumble drying because heat can be tough on elastic and lace. If a bra feels damp after wear, let it fully dry before putting it back in the drawer.
When to replace everyday bras.
If the band rides up even on a tighter hook, the cups gape differently than before, or the elastic no longer recovers after washing, it may be time to replace or refresh the rotation.