that's because it was a full blown relational database - it literally shipped with a desktop variant of SQL server (MSDE) and the WinFS bits were implemented in .NET on top of that.

I recall installing the WinFS beta 1 release and suddenly the winfs-related background processes were eating up 150MB+ of RAM at a minimum, even with no stores created or files indexed - when machines back in 2005 had 512MB of memory that's actually a lot for what is supposed to be a background service.

Windows XP back then only needed 128MB of ram to run. they made a mistake in not building it on top of something akin to sqlite - hell they could've implemented maybe 70% of what they shipped in beta 1 with just sqlite alone.