Tl;dr - OSS licensing is important
"Hey, from a legal perspective, are copyright notices worth the effort to get right?"
In the same way that paying fees is usually a condition of a proprietary licenses, often correct attribution is a condition of FOSS license. So, in one sense, not doing it or caring to get it right is like not paying for a license.
And, it can lead to you getting sued. Apart from OSS warriors (who will sue for principle), a clever competitor can also take a swipe, as CoKinetic did at Panasonic Aviation (google it).
Breaching FOSS licenses is awkward, especially if you use a lot of FOSS, or happen to be a vocal supporters of the OSS community. Wix epically embarrassed wordpress for incorrectly applying GPL (google it).
I wonder if FOSS attribution and 'admin' is really such a big pain and what I (legalite) can do to help beyond a robust compliance program...