I walked in my high school graduation because it didn't occur to me that not doing so was an option (I was valedictorian so I had to speak). I did NOT walk in my college graduation. Honestly not a big deal. I had a small school (about 50 in my class). My brother had about 800 in his class. I can definitely see not wanting to sit through that!
I'm a teacher who lives in a college town and I think this is pretty typical. A small percentage of high school grads don't walk because most don't realize that it's optional. At the University ceremony a much greater percentage choose to skip it.
I walked at both but would have skipped college grad had it not been very important to my DH. He sacrificed for me to go back and finish so if he wanted the ceremony then I felt like he deserved it as a thank you for his support. My DD21 will graduate college next year and I will definitely pressure her to walk, if necessary. DH and I have sacrificed, and spent, a lot for her debt free education and we want the ceremony even if she doesn't. She hasn't mentioned skipping it, though.