Google+ has had a hard time, mocked by many it has struggled to find much of an audience in the shadow of Facebook. That reason is probably why a number of services will no longer need a Google+ account to access, with reports saying that the photo service will be next. As of April 1.5 billion photos were uploaded to Google+ every week.
This number will presumably increase if the service is opened up to users who only have a regular Google account. Personally I think this is a good thing, since it’s always baffled me as to why Google prevented you from using features unless you had a Google+ account (like YouTube comments, or leaving a review on Google Play). I know it doesn’t take much to set up a Google+ profile, but most people don’t need another social network to think about.