the dollar sign convention predates NT, it's one of the things inherited from Files-11, where the metadata-files were not hidden from end user, just marked with strict enough permission checks. (A lot of VMS APIs used dollar signs for namespacing, too, and I believe some aspects of the naming scheme come from specific PDP assemblers when referring to some names?)

Looking at NTFS from on-disk structure side, it always seemed quite obvious to me that a lot of accolades given to BeFS applied to NTFS - it's the lack of actually using the abilities - and IIRC a lot of the indexing system is actually used by Windows Search, which in tech spaces I always found mentioned as "useless thing I disabled", yet I found out later offices where people are very much dependant on the component (helps that MS Office installed document handlers to index its documents in it)