Google finally did something about that. You can now invite parents and guardians to subscribe to a daily or weekly summary of activities in your Google Classroom classes.
Initiating the process of sharing summaries with parents and guardians does require cooperation on the part of your school's administrator. Administrators must choose who can invite parents and guardians to receive summaries. A parent or guardian only needs to be invited once regardless of the number of teachers his or her student has. In other words, parents of middle school and high school students don't need to be invited by every teacher that his or her student has.
Once a parent has been invited by the school, teachers can choose to enable sharing of summaries with parents. Teacher also have the option to send emails to all parents from Google Classroom.
Read the complete set-up directions for class summaries on this help page written by Google.