Did those people sign a legally-binding end-user license agreement?
Because what I see is essentially "they're storing stolen property" but the burden of proof is on the author to prove it was, indeed, stolen.
I imagine the bar for that is pretty high otherwise anyone could weaponize DMCA to target their competitors' repositories.
You seem to be thinking about "adblocker running in browser", since you brought up EULAs.
That's not what OP alleges - they are saying people are redistributing modified versions of OP's copyrighted code. DMCA is an appropriate measure in such a situation, but it's unclear why OP's DMCA takedown was rejected by GitHub. Without more detail, it's hard to comment further
one would think, if it is still up there, OP might point us at it so we can see for ourselves, right now it's "trust me"