It used to be SAHMs who had a bit of spare time while the DC were at school, or who had never worked so had more time to give when the children flew the nest. Most mothers work now, or have commitments at home.
Retired people used to volunteer, but are now called on to help with grandchildren childcare.
Older volunteers paused during covid and don't feel comfortable returning.
Most of the volunteers at the charity I work for are linked to faith groups where the volunteering bug is ingrained.
We also get fabulous teams of volunteers from local businesses to do ad-hoc projects.
Teens who are doing DofE are are great source of committed volunteers, albeit 1 hour a week.
It takes a lot of time and expense to manage charity volunteers. But the commitment, generosity, expertise and positive attitude can be priceless.
Personally, I volunteer at PTA, Parkrun, School Governor and the occasional community event. I encourage my DC to volunteer when they're not too busy with exams, as I think it's a positive way to be part of a community.