Fall collections are shown in winter and spring collections in autumn, which appears perverse from outside the industry. The lead time is filled with work that has to happen in sequence.
Buyers order before anything is made
Runway shows and the appointments around them exist so that wholesale buyers can place orders, not primarily so that consumers can see the clothes.
Nothing is manufactured in quantity until those orders exist, because producing a full range speculatively would tie up capital in garments that may not sell.
The show is therefore closer to a trade event than a launch, and the retail arrival months later is the actual product reaching customers.
Mills work on their own lead times
Fabric is not held in unlimited stock. Mills schedule production runs, and a specific cloth in a specific color must be booked and woven before garments can be cut.
Yarn dyeing, weaving, finishing and shipping each consume weeks, and delays at any stage push everything downstream.
This is why fabric decisions are locked long before final designs are, and why a late change of cloth can remove a garment from the season entirely.
Production capacity is booked, not summoned
Factories allocate their lines across many clients, so a brand competes for slots against everyone else working to the same seasonal calendar.
Missing an allocated window can mean waiting for the next opening, which may fall after the selling season the garment was intended for.
Ocean shipping from producing regions to American distribution centers adds several more weeks, and air freight is used only where the cost is justified by the delay avoided.
Retail needs the goods early
Stores put seasonal merchandise on the floor well before the weather turns, because full-price selling happens at the start of a season rather than during it.
Markdowns follow on a schedule set in advance, so an item arriving late enters the calendar partway through and sells at reduced margin from the outset.
That pressure pulls delivery dates earlier still, which is why heavy coats appear in stores during warm weather and swimwear during cold.
The system is under strain
Shows are now visible to consumers immediately, which creates demand months before anything can be bought and dissipates it before the goods arrive.
Some brands have responded by producing part of a collection in advance so that a selection is purchasable at the moment of the show.
The approach requires accepting production risk on unsold inventory, which is why it has spread among houses with the capital to absorb it and few others.