The subs wouldn’t exist without the original work.
Edit: Yes, it’s a subset of the script and not thee script itself, and being a pedant about that isn’t a useful point. It’s just pedantic.
Imagining I were to hand you a book. It's Harry Potter but missing every third sentence. You tell me "It's Harry Potter" and I'm like "nuh uh", I'd be just being a pedantic ass and not making a good point.
Similarly, I might pay for a subscription to a website which has a detailed review of that episode along with screenshots. Neither replace watching it, not even close.
I do think that subs are a little bit more legally ambiguous than a review but I think you could make a reasonable argument that they're a fair use under US copyright law.
Movie scripts contain much more than the dialogues. There's enough of an argument to be made that transcription is covered by fair use rights.
source: I worked in the music biz
Calling the subtitles "basically a script" is like saying JavaScript is basically Java.
Things like [ominous music plays] are not part of the script at all, but featured in subtitles