On relicensing etiquette

Almost 10 years ago, I wrote a simple throwaway script to migrate book collections from Anobii to Goodreads. Because I thought others could use it, I slapped a MIT license on it and released it. Back then Github was just a fledging startup (I didn't even open an account there before 2010). Later on, Alper Çugun helpfully updated the script and uploaded it to GH, so that more people could use it. Great! People started forking it and tweaking it, as they should. Except...

Uhm. There is one requirement to abide to MIT terms: keep the original copyright assignment. Apart from that, you can rip the code inside out and nobody will care; you can even relicense it to your heart's content (and someone did exactly that, re-releasing it as GPL - unfortunately, he also dropped the original copyright statement). Just leave the original copyright notice somewhere, and you're golden.

I've kindly let "infringers" know that I'd like them to reinstate the original credits -- it's just polite, and anyway everyone can see from GH commit history that they're being silly. Why do people do this? How hard is it to just add your own © line, or keep the original statement buried somewhere? Sometimes I just don't understand People.