iCloud has two ways to share photos with friends and family, but you cannot share an iCloud Photos Library. You can share the storage in iCloud with family sharing, but the data you are storing in iCloud can only be shared in a very limited way.
- Shared album: To use Shared Albums, you do not need to subscribe to paid Cloud Storage. They are free. And that is why they are limited. Also, they should only be used to show your photos and videos, as they will limit the resolution to 2048 pixels at the longest edge of a photo, so you cannot share photos and videos in the full resolution.
- Shared folders on iCloud Drive: You could export your albums as folders on iCloud Drive, then ctrl-click the folder and use the command "Share > Share folder".
As to your question: "Why can't I simply give read-only, downloadable rights to anyone with an icloud account? " Apple has developed the Photos.app and the Photos Library as a single-user database. iCloud Photos is a syncing service to keep our Photos Libraries identical and updated across all our devices, while keeping our photos private. we can share photos with others, but selectively. We are supposed to pick our best photos and share them individually with the handpicked persons who might be interested in them.
If you want a network photo library to be shared with several people, for collaboration on your photo projects, you need a different software. I do not know any to recommend, because I prefer to keep my photos private and only to share my best photos, selectively. And when I share an album, I do not give write access to the subscribers. It will usually result in others dumping thousands of photos into the album and making it unusable.
