I think this idea rests on the false premise that people both need and have a right to pornography.
Many adults go about their lives without accessing it/getting off on it. It’s not a human need like food or shelter. So government isn’t going to become a supplier. Parallels could be made, I suppose, with safe injecting rooms and methadone clinics etc - but that’s a medical/health service that protects both the individual and the community. I don’t think the same argument could be made for a government sponsored porn bank.