The high cost of production is severely limiting which operas are available to the public.
Conclusion
The author wants to ditch the big corporate sponsors so opera companies can produce more obscure operas.
Evidence
The corporate sponsors are the ones forcing only-the-greatest-hits programming.
Evaluate
The author treats corporate demands as the only thing standing in the way of obscure operas. But there is a quieter possibility: famous operas might be the only ones that bring in enough ticket sales and donations to pay for themselves. If that's true, cutting the corporate money doesn't free smaller operas — it just shrinks the budget so much that only famous operas remain affordable.
Goal
The right answer will show that without corporate sponsors, opera companies still couldn't afford to produce anything beyond the famous operas.