Another limitation for what you want is that it shows the map markers only for the events that are listed for that particular page, 10 activities per page.
It won't all at one time show all of the activities that you have uploaded if it exceeds 10 different starting spots.
Then enter something in the Starting Near box, like the zip code of where you start most of your runs. Unfortunately, this is where the biggest limitation is, because if you choose too large of a search area, you will get an error. I tried entering "United States" and then "Virginia" and I received errors that my search area was too large. This is a known issue that's been around for a long time. Hopefully they will improve this, but in the meantime, if you narrow it down to a city, it should work.
I discovered that if you search for your own username and leave the "starting near" box blank, you can retrieve all of your activities. At least that works for me, with my rally rides scattered all around north Texas and southern Oklahoma.
That doesn't work for me. If I leave it blank, it reverts to "current map view." I think you just happen to the current map view set to north TX and southern OK.
Mine doesn't work if I have even a single blank character in the Starting Near box. The box has to be completely null for it to work for me (a double click clears it). And then it will switch from the current Garmin default in Australia to my area and my rides.
Ah yes, good point.
A long time ago I suggested that it would be great to be able to see all of our own activities on a map. I travel a lot and I thought it would be neat to see where I've run (and biked). On TripAdvisor, I can see a map of the world with pin drops on all the places I've been, and it would be neat to see something similar on Garmin Connect for all my activities.