Although there may be some packages that prove the exception to the rule, generally speaking packages for Sublime that require external tools in order to work require you to install them yourself, and they just provide the glue layer between the external tool and Sublime.
If they tried to install everything you needed, things would quickly spiral out of control (e.g. it would also have to determine where
npm was in order to install
jshint, which might require it to install
node on your machine, which would require it to ask you where you'd like to install it, and all of that work has already been done by the people that make
In particular, the documentation for SublimeLinter-jshint says:
Before installing this plugin, you must ensure that jshint (2.5.0 or later) is installed on your system.
To install jshint, do the following:
Install Node.js (and npm on Linux).
Install jshint by typing the following in a terminal:
npm install -g jshint
[ ... snip ... ]
In order for jshint to be executed by SublimeLinter, you must ensure that its path is available to SublimeLinter. The docs cover troubleshooting PATH configuration.