Being a GP is far from glamorous. It reminds me of customer service. Instead of answering phone calls, you answer pms, investigate reports, etc. If you want a free weekend, be ready to commit longer hours during the week. To be frank, the job is a bore.
That being said, I find value in doing it. I can safely say on a weekly basis that I've prevented cyberbullying and sexual harassment on a game I enjoy. Would I have applied if the job description was solely to approve uploads, host events and monitor hackers? Most likely not. These all go on the back-burner when the more serious reports come up.
As to the manning issue. If a grade school didn't have the personnel to monitor recess several days a month, you wouldn't go yelling at the parent volunteers ;you would contact the school administration. Whether a GP does the minimum amount of hours or 25-30, I respect the work they put in the server equally. They may be easy to blame yet they are not the ones at fault if the server is not monitored 24/7. It isn't rare for a member to put 30 hours a week. Heck, I've even seen someone do 80. They have no obligations to be policing and by doing it, I find it makes them far from lazy asses.
A volunteer finds value and time to do a task. Increasing the minimum requirements would dissuade the people who join for the right reasons. Hiring more people would be a better solution.