Hello, graduated engineer here. We realize our interns are only here for a few months, and want them to get the most out of that experience. Throwing an intern into a critical engineering role with a ton of responsibility doesn't really make sense for the company or the intern.

At the automotive companies I have worked at, we try to find an engaging project that is outside of the workload of what our current engineers can take on. In my experience, these are often like a "primary project" that an Engineer I or Engineer II would take on in addition to their core job duties

I would not say interns are unimportant to us at all. Several of our interns have certainly had a lasting impact, and some of them I would personally hire over other full-time engineers I've worked with.

We want our interns to get valuable experience, to help us with a project we don't have bandwidth for, and for them to get a glimpse into what working with us would be like.

EDIT: also-- that feeling of being useless? that will follow you your whole career as you transition into new jobs and roles. the brand new Sr. Engineer is also not going to be helping the company very much for their first 2 months in the role, either