Have you laid a straight edge on the rim? Say a credit card oriented radially. Those rim sides (the braking surface) started off flat. I'll bet the middle of the braking surface now makes a channel perhaps much of 2mm deep. That's aluminum that once kept your rim strong and is now distributed along those 10,000 miles.
Now, both broken rim portions, drive and non-drive are pushed to the drive side? Weird. Weakened rims from brake wear typically explode outward and usually violently. You do not want to be riding and have flesh in its path. (Calves of legs.)
If this failure is from brake wear, not how deep the channel is and in the future, never get within (oh, say) 2/3s of that dept Riding conditions have a lot to do with how fast rims wear from brake use. Road grit speeds it up a lot. Wet roads means more grit sticks to the rims. The sand and dust of different regions can be quite different in abrasive qualities. Those of us who ride in the Pacific northwest in winter see brake wear at very high rates due to the lava dust that is everywhere. In my commuting days, I wouldn't go two full winters on a pair of rims.
A thought - it looks like both sides are worn but only one side has cracked through. So cracked through side has bulged out. Intact side is worn in. (All tough to judge from the photos without having seen the bike.)