Two things can be true:
Mike Brown never had any intention of trading him, so he set the bar where it knew it would never be met.
Hendrickson is probably worth a first.
Why is Hendrickson only worth a second, but Myles Garrett would have fetched multiple firsts? I know Garrett is the better player but, at least based on production over the past 5 seasons, the gap is not that big. I think people, including NFL GMs, still take draft positioning into account when assessing value.