this would explain why this is never done"

So would lots of other things. How often do we see ships being boarded in Star Trek when they haven't already suffered enough damage to take down their shields, and possibly take down their transporters too?

In situation like that, the crew has enough things to cope with other than trying to lock on to hostile individuals within their own ship, who are probably moving around, and don't have handy Starfleet com-badges to focus on.

this would explain why this is never done

So would lots of other things. How often do we see ships being boarded in Star Trek when they haven't already suffered enough damage to take down their shields, and possibly take down their transporters too?

In situation like that, the crew has enough things to cope with other than trying to lock on to hostile individuals within their own ship, who are probably moving around, and don't have handy Starfleet com-badges to focus on.