lsof was written by vic abell, who also wrote a graphical java gui for it, glsof.
Sloth exists only on OSX and is a GUI app.
I’d ask the opposite: Any reason anyone would anyone use Sloth over lsof?
lsof is pretty common, but I don't think it is actually standard in any way, for example it is not part of POSIX or SUS which arguably are the two most influential UNIX related standards.
http://bhami.com/rosetta.html (ctrl-f lsof)