Since old times, UNIX philosophy has been "building short, simple, clear, modular, and extendable code", so a super-tool that kills based in port number is way too complicated to maintain, on the other hand, `kill` was meant to send signals to the process (which happens to end them) not necessarily "to kill" them.

I have searched for a tool that do that, none found that only do that (normally they comes bundled with other tools/functionality or are complex of use). Of course you can use <code>kill -SIGNAL $(lsof -i:port)</code> to send any signal you like.