Marketplaces that store and ship on a seller's behalf charge by size and weight band rather than by the exact item. Those bands push product design and assortment in directions shoppers rarely connect to fees.
Fees are banded, so thresholds matter more than dimensions
A fulfilment charge is set by which category an item falls into: small envelope, standard parcel, oversize and so on. Within a band the charge is flat.
That makes the boundary between bands the only dimension that really counts. An item a fraction over a threshold pays the same as one much larger.
Sellers therefore redesign packaging to sit just inside a band. Slimmer boxes, flat-packed contents and removed inserts are usually fee engineering rather than environmental policy.
Storage charges punish slow-moving stock
Warehouse space is billed by volume and by time, and the rate typically rises for inventory that has sat unsold for many months.
A slow seller that occupies a large footprint can therefore consume its own margin while waiting for a buyer. The longer it stays, the worse the arithmetic gets.
This is why bulky, slow-turning goods vanish from marketplace catalogues before peak season. Sellers clear the space for items that will turn over quickly during the busiest weeks.
Low-priced items become uneconomic
Handling cost does not fall in proportion to price. Picking, packing and shipping a low-value item costs nearly as much as doing it for an expensive one.
Below a certain price the fixed cost consumes the entire margin, and the listing stops making sense at any volume.
That is the mechanism behind multipacks. Bundling several units raises the order value above the fixed cost without changing the handling work involved.
Returns are charged twice over
A returned item incurs the outbound cost, a return processing cost, and inspection before it can be resold. Some units cannot be resold at full price at all.
Categories with high return rates, clothing especially, carry that expected cost in the original price. Everyone pays a little so that the returns can be absorbed.
It also explains why some sellers refund without asking for the item back. When processing costs more than the goods are worth, retrieving them destroys value.
The fee schedule shows up in the catalogue
Taken together, these charges favour compact, high-value, fast-selling goods with low return rates, and they steadily push everything else off the platform.
Shoppers notice the result without seeing the cause: heavy or awkward goods are easier to find in physical stores, while small dense items are cheapest online.
The assortment you browse has already been filtered by a fee table before you ever open a search box.