This is *not* a minimal working example, neither it’s minimal nor it’s working.
You can fix this by replacing the \\ with \crlf to add a linebreak in the entries:
\define[3]\MVC
{\starttabulate[|l|lp|]
\NC Model: \NC #1 \NC\NR
\NC View: \NC #2 \NC\NR
\NC Controller: \NC #3 \NC\NR
\stoptabulate}
\starttext
\MVC{usedmodel}{firstViewFromSeveral\crlf secondViewFromSeveral\crlf thirthViewFromSeveral\crlf fourthViewFromSeveral}{usedController}
\completecontent
\MVC{usedmodel}{firstViewFromSeveral\crlf secondViewFromSeveral\crlf thirthViewFromSeveral\crlf fourthViewFromSeveral}{usedController}
\stoptext
Wolfgang