people who want to statically link SFML probably also want to statically link the VC runtime library.
I don't think this would be an accurate assumption.
The VC redistributable runtime library, once installed, can be easily shared amongst many programs. SFML libraries, however, have a few problems with that so often end up being stored alongside executables.
"Installing" SFML so that it can be shared is troublesome not least it can be difficult to determine which version is installed and there isn't much in the way of a standard way to locate or name them so multiple programs wouldn't share them. Avoiding sharing the DLLs with the executable is an understandable reason for people to want to statically "link them away" (although, DLLs in the folder aren't really going to harm anything, are they?).
VC redist, though, are installed identically on all systems and all versions are kept entirely separate. If one program installs this, all other programs can use it easily.
Whether you allow your installer to install the VC redistributable automatically or just give out the link, it's simple enough for the user to install.
That said, there are, of course, times when people do want to statically link the redist. Who is to say whether or not that is with statically linking or dynamically linking SFML?