It's all perspective again made to suit an agenda ... i use a very similar app to watch the commercial fishing boats.
1) the dots/arrows stay roughly the same size so places with high traffic or other places in shortish proximity will look very dense but there could be 20k between em until you zoom in
2) it will show inactive boats going back hours or days, a German frigate could have passed through on Friday and if his tracker bleeped in the channel it will still be showing. The arrows are the active boats; the fact there's lots of dots means there's very little activity
3) li