Why don't the pros kill the scouting probe as it passes through their mineral line?

While watching pros play (MLG, GSL,etc) I notice that sometimes a player will move a probe/drone/scv right through the other player's mineral line. I have yet to see a pro try to kill this drone as it passes through.

When someone does this to me, I often have my drones all attack the scout, killing it pretty much instantly. I am only gold, so if I can manage to do this often, I am sure a pro could. Is there a reason they don't? I know I lose mining time, but I feel that I gain by not having to worry about what that scout is doing, esp if it is a probe or scv that could be used to harass my early hatch.

Sending all your workers to try to kill a scout; even if it's already in your mineral line, will probably put you down more than the 50 minerals your opponent lost, as that could be 5+ seconds times 10-15 workers. At 43 minerals/worker/minute, that's barely break even, plus you might be losing the opportunity cost of spending your APM elsewhere.

So the problem you're running into is that you're trying to kill a Gold Level Scouter. Most people as this level only queue up a few way points and go back to their base to do something else. Often times they'll do silly things like send their Probe right through your mineral line, instead of around the back, or ignore their Probe until it takes a hit or two.

Once you get to higher levels you run into people who have higher micro skills and avoid obvious traps like those you're describing. Even though you'll occasionally get a surround on them they know things like the mineral trick (harvesting from a Mineral patch gives harvesters unit walking) and easily avoid death.

More often than not, killing a Probe (before you have attack units) is a waste of your time unless its trying to become bothersome.