A venue, a caterer and a photographer will frequently quote more for a wedding than for an identical event held on the same day. The gap reflects the position the buyer is in.
The buyer is inexperienced by definition
Most people organise one wedding, so they have no baseline for what any component should cost and no relationship with any supplier in the category.
Corporate buyers commission events repeatedly, compare quotes routinely and negotiate from knowledge, which disciplines what suppliers can charge them.
A market where nearly every customer is a first-time buyer supports prices that a market of repeat buyers would not.
The date cannot move
Once invitations are sent and other suppliers are booked, the date is fixed, and a supplier who becomes unavailable or raises a price creates a genuine crisis.
That removes the buyer's strongest lever, which is the willingness to walk away, and suppliers price the certainty of the booking accordingly.
Deposits and cancellation terms formalise it, since money committed early makes changing course expensive as well as stressful.
The service really is different in some respects
Weddings run long, involve alcohol, mix groups who do not know one another and have no possibility of a second attempt if something fails.
Suppliers staff accordingly, bring backup equipment, arrive earlier and carry insurance appropriate to an event where mistakes cannot be corrected later.
They also block the whole day rather than a few hours, so a Saturday wedding is the only booking that supplier takes.
Emotional stakes suppress price sensitivity
Spending decisions are made in the context of a once-in-a-lifetime framing, and an upgrade costing a small fraction of the total reads as trivial in that context.
Suppliers present options in packages that make the incremental step small relative to what has already been committed, which is effective precisely because the total is large.
Social visibility adds pressure, since the event is judged by guests in a way an ordinary party is not.
The premium is not universal or fixed
Suppliers with more weekday availability, venues outside peak season and newer businesses building portfolios all price closer to the general market rate.
Couples who separate the components and book them individually, rather than through a single coordinated package, generally pay less for the same result.
Which suggests the premium is attached to the way weddings are bought at least as much as to what is delivered on the day.