The cost is built into the performance
An opera is expensive before the audience takes its seats. A company must pay singers, musicians, stagehands, and other staff for rehearsals and performances; it also has to build or rent scenery and costumes, maintain a venue, and coordinate a large production. Many of those costs are fixed: adding another performance may bring in more ticket money, but it does not eliminate the expense of preparing the show.
That makes a production hard to scale like a cheaper event. A small audience does not let the company shrink the orchestra or stage crew in proportion, and there are only so many seats to sell. Raising prices can help, but it risks pricing out the very audience a company wants to attract.
The budget is broader than ticket sales
For many opera companies, tickets are only one part of the financing. Donations, grants, public support, and income from other activities can help cover the difference. This is not necessarily a sign that a production has failed: such support is often part of the operating model, paying for an art form whose costs are high and whose ticket income has a built-in ceiling.
The tradeoff is that a company must balance artistic ambition with financial risk. A large cast or elaborate staging may make a production compelling, but also raise the amount that must be recovered from a limited number of seats. The curtain can rise because the company has assembled several sources of support—not because ticket sales alone made the show pay.
