Earlier quoted context omitted.
Most open source licensing requires 0 citation. If I copy your formula or recipe, I don't need to cite a thing - you don't own the copyright to your own formula. I could sell your work if I wanted to do so. Plagiarism, as it affected my grading, was copying without attribution. Attribution is rarely required for most licensing, except where it is. These sorts of distinctions are lost in the collegiate machine.
Which open source licenses are you talking about? The most common that I can think of is GPL, which does not allow you to remove the copyright notice, although you may add yours in addition to it. The next one that comes to mind is the BSD license, which states: "Redistribution and use in source and binary forms are permitted provided that the above copyright notice and this paragraph are duplicated in all such forms…
Plenty of people copy code straight off of blogs, which due to the DMCA are given implied copyright. Stackoverflow, also, requires attribution under the CC license, but nobody attributes stackoverflow when applying fixes to their problems.
If I include an MIT licensed JS file, I can replace functions willy nilly, or rewrite parts of the code. If it's LGPL3 or GPL, I can't.
Licensing is more nuanced than you're describing, but pragmatically I never need to cite anything. The most I need to deal with licensing is handling proprietary code (unlicensed github code, for example), and GPL/LGPL.