Trust is the whole issue in this category. Photographers are rightly suspicious of contests that quietly claim rights to their work, and the entry-fee-harvesting operations have made everyone cautious. An address that looks institutional helps enormously with that, which is why competition organisers gravitate toward the .org in the first place. This is the exact term on the right extension. The economics are real: entry fees, sponsorships, print sales, and a permanent supply of photographers looking for somewhere to submit.