At most large concerts the merchandise queue is dramatically longer and slower than any bar queue. The difference is a throughput problem rooted in what each transaction requires.
The transactions are not comparable
A bar sells a small number of items at fixed prices, handed over immediately. The exchange takes seconds and requires almost no conversation.
A merchandise sale involves choosing a design, choosing a size, checking availability, retrieving stock and completing a larger payment.
Even performed efficiently, that sequence takes several times as long. The queue length is mostly this difference multiplied by demand, which is why adding a second stand helps far less than people expect.
Stock cannot be replenished during the show
Bars restock continuously from cellars and stores behind the counter, and running out of one product rarely stops the queue.
Merchandise arrives in a fixed quantity per venue, sized and printed in advance. When a size sells out, every subsequent customer has to be told and has to decide again.
Those interruptions compound. A stand with depleted stock slows down precisely when the queue is longest.
Staffing is sized for a shorter window
Bars operate for the whole event and are staffed accordingly. Merchandise demand is concentrated into the periods before doors, during changeovers and immediately after the final song.
Staffing for those peaks would leave people idle for most of the evening, so stands are staffed for an average that the peaks overwhelm.
The result is predictable congestion at three specific moments, which is visible to everyone including the operators. The post-show peak is the worst of the three, because the entire audience becomes available at once.
Scarcity is deliberately part of the product
Tour-specific and venue-specific items are printed in limited numbers, and that limitation is what makes them desirable.
The same scarcity guarantees that some buyers will be turned away, which converts a queue into a competition and encourages people to join it earlier.
Nothing about this is accidental; it is the same mechanism that governs any limited release.
Pre-ordering has only partly helped
Many tours now sell merchandise in advance for collection or delivery, which removes some demand from the venue entirely.
It works less well for the impulse purchase, which is a large share of concert merchandise and depends on being at the show.
Stands with dedicated collection points and card-only payment move faster, and the difference is measurable, but the underlying transaction remains slower than pouring a drink.