once again, i will ask: why do people care so much about only having one <details> element open at a time? let me see what i want to see!

Yes, absolutely, and UX experts such as those at the Nielsen-Norman group have for years been advising against auto-closing the already-opened options when opening another. For good reason - user frustration in their research.

If I clicked it to open it, then if I want to close it, I'll click it again. Don't hide content I might still be reading!