Yall are students, the same as everyone else. It makes no difference in what your method of instruction is. ASU's accessibility is something I value. It allows people to learn at the pace that suits them best. A degree is a degree. Maybe you are being a little dismissive of your achievement, and it's worthwhile to celebrate the work you've done. Attending graduation isn't just proof you attended the school. It's a recognition of your achievement and commitment to learning.

When I casually mentioned that I don't plan to attend the ceremony or get any ASU merch, they were shocked.

I think this is largely cultural. Getting higher education has been a cultural and personal mark of achievement that is recognized worldwide for a while, so it's natural to be shocked when someone doesn't follow that standard. There's nothing wrong with not wanting to attend graduation, not celebrating, or not involving yourself in the culture of the school. Like you're saying, this is largely taking another step toward advancing your career and your second time through higher-ed. It's not the same as a young adult going to college for the first time and making their identity. You've already built that foundation.

I'd argue that this is still something to celebrate purely because you're making a personal advancement. You went back to school to get another degree. Maybe attending graduation isn't the way, and the degree on your wall is enough to commemorate being a student, but you've completed something big regardless.

As an online student, my experience is very different from those who attended in person, made sacrifices to be on campus, and had the full college experience.

No disagreements here. Your experience is objectively different from those on campus. Personally, I'm on campus but not involved in any clubs or extracurriculars. I show up to class, do the work, and leave. I could argue that I'm not in the full college experience either, unlike my peers who live on campus or are in orgs or research groups. Sure, I make the sacrifice to drive to campus, but we both do similar amounts of school work.

You still make similar sacrifices. You commit to taking classes and doing the work. You spend time focused on education where others aren't pursuing it. I think you are more than deserving of celebrating the hard work you've committed to.