Why does Arc proxy shared URLs via arc.net?

I noticed that all highlight URLs on Arc use a redirect via arc.net.

I don't see any technical reasons for that, but with my experience with ad-tech and (later) privacy I can think of a few of reasons why this is happening (TL;DR data collection).

I would like to explore this subject further and summarise what I've learned in writing. I want to make sure I'm not unfair here, hence the question.

Can you think of any valid reasons why this feature exists as an opt out?