All that kmz files we can create your own custom map and share with your friends. one more thing it'll help you as a layer on Google map maker too.
First you need to upload the kmz file to Google Maps. This will save you the custom map and it could be your reference link for every edit to that.
Open your Google Drive to find the track file from "My Track" folder.
Download your track file.
Launch your web browser then type: maps.google.com
Click on the gear icon then select "My Places"
Click on "Create with classic My Maps"
Rename your custom map in "Title field", give some description in "Description Box"
Then click import.
Click "Choose File" then browse to the file you downloaded from your drive then upload it. So after upload you will get your own custom map.
Note: Refresh the tab to see you kml file.
Now you got your custom map and also kml file for a reference in editing on Google map maker.
You can copy this kml file to put as over lay in google map maker.