Weddings are a lot more work for service professionals than other events. The drive to get everything right for a once-in-a-lifetime-event takes means more meetings and pressure. For example, a florist describes the difference between a corporate event and a wedding in a Huff Post article.
A corporate event usually involves a couple phone calls and maybe a sample arrangement, she said. The florist then drops the arrangements off at the venue and their work is done.
“When a wedding comes around, it’s not that at all,” she said. “We
explain to the client that we have multiple phone calls, in-person
meetings and then sample meetings with an entire table set-up. We’ll
have constant back-and-forth email exchanges, probably up to 40 or 50
Furthermore, there is variance in how intense the bride and groom are about getting every detail correct.
Almost all weddings are more work for the vendor than a corresponding
business event. They are usually not 3x the work but usually at least
50% more work. However, every once in a while the vendor gets a
really high-maintenance wedding that it is 10x the work (the
"nightmare" client). This high-maintenance wedding has a wedding
couple that is bickering, dueling parents, and super high emotions.
Because of the occasional "nightmare" wedding, vendors need to
increase their prices for everyone so that the vast majority of people
end up subsidizing the few high-maintenance ones. (source)
Wedding professionals can't identify the difference between reasonable couples, and impossible ones, so they have to charge higher prices for everyone.
Since couples do actually have lots of options on locations and vendors competing for their business, the more work explanation makes more sense than some sort of monolithic wedding-industry-cartel colluding to increase prices across the world.
Another plausible explanation does involve wedding vendors profiting. The idea is that demand for a specific venue or cake artist is inelastic, insensitive to price. Once a couple sees that beautiful red barn with fireflies and imagines all their friends and family drinking from mason jars there, they might no longer see other alternatives as good substitutes. They'll be less likely to balk at the price tag and go elsewhere. This New York Times article describes the problem:
Which brings us to the matter of those wedding-dream-board makers.
Strong consumer preferences — about the flower type, bridesmaid dress,
cake decorations, music style, whatever — mean less price sensitivity
(what economists refer to as greater demand inelasticity). If the
cocktail napkins must be blue, the happy couple will be willing to pay
more for blue. So if there are enough brides out there with strong and
specific preferences, who want their weddings to be the special day
they always dreamed of, that’s going to push equilibrium prices
higher, no matter how transparently they are displayed. In other
words, the Bridezillas keep prices high for the rest of us.
This explanation also makes sense, even in a competitive environment. A venue owner would only lower his prices to help book more weddings. If most couples aren't booking primarily based on price, the venue owner is less likely to entice couples away from other venues with lower prices. This leads to higher equilibrium prices. Meanwhile other non-wedding events are hosted by people far more sensitive to price, so it makes sense to keep prices lower for them in order to keep the venue booked every day.