The file picker on Windows should be thought of as more like a process than a function call. It has to 1) read the metadata of the current directory’s files 2) look up which icon to use for each 3) load the icon 3) call apps that may modify the file icon overlay (like “synced” or “not synced” cloud icons for Cloud file systems like Google Drive) 4) read the registry for various settings 5) load which pinned files a user set up - etc etc. All this involves dozens of disk reads, calling into third party code, etc. A lot of this may be cached but who knows.

The alternative to this is to roll a barebones file picker - there might even be one available in the Windows API.