You only need to feel guilty if you don't care about what your kids are doing.
Mothers don't get any awards for perfect attendance (... do they?). Your real objective is to support your children.
My husband's niece has four very active girls. Mama and Daddy have to divide and conquer most of the time, with Mama going to, say, the pep rally and Daddy going to the game, or Dad going to one girl's game on one side of town and Mama going to another girl's game on the other side of town. The baby of the family (age 2) is learning more about girls' athletics than most kids her age!
If you have relatives living nearby, maybe they might like to be on the support team and go to some of the events when you can't. If you don't, maybe you could talk with your active children and find out what things are most important to them, as far as your attendance is concerned.
The idea is for your children to feel confident that their parents care about what they're involved in. If your children know you care (and it sounds as if they do), you're doing a good job. SAHMs have only 24 hours in a day, too, just like everybody else.