The term "junk DNA" was coined very early in our understanding of DNA. Even when we had no idea what it was for, very few respectable geneticists actually believed it was "junk" - basic evolutionary theory argues pretty strongly against it. But the name has stuck around for far longer than it deserves to.
>basic evolutionary theory argues pretty strongly against it.
That's not true. Over millenia leftover chunks of DNA can accumulate for no good reason. Duplication mistakes, viral infections etc. The term junk dna originated from the initial assumption that all noncoding dna was useless. Evolutionary theory has nothing to do with this.
There is a huge difference between "large parts of it are useless" and "all of it are useless". And large parts of the non-coding DNA are probably useless, unless you're extremely generous with what counts as "function" when examining this.
Evolutionary theory says that it would not be preserved if it wasn't being used. If it was never read or relied on, then random errors would accumulate dramatically faster than in coding DNA. Because in coding DNA mutations generally lead to problems and so they're selected against.
IIRC, much of these non-coding sequences (so-called "junk DNA") are preserved in a way that shows they are being relied upon for something.
Basic evolutionary theory may argue that most of it is "junk" in the sense of being non-functional (even though some may be species-specific or under selection too weak or recent to be detectable). One paper that lays out this argument has title with the memorable beginning "On the Immortality of Television Sets." https://academic.oup.com/gbe/article/5/3/578/583411
