Roger's list of 5 ways to get a parent to be a coach here:
Time with your kids. We all have busy schedules, so the time with our kids is limited. When you volunteer with your kids' teams you basically schedule in more time with them. It might not be one-on-one time, but it will be memorable time for you both.
Your help is needed. Having a group of 8-plus kids together doing anything is challenging. Whoever volunteers to be the head coach can use all the help he/she can get.
You have a chance to impact kids. Years from now the kids you coach today will still view you as their coach. They will remember the time you had together enjoying sports. By volunteering, you could be the mentor a kid needs to set him/her on the right course in life.
You will grow great relationships. You will meet some pretty good people through volunteering to coach and grow some relationships deeper. Coaching has benefits for the kids as well as the coaches.
Your kids will appreciate it.