Looks like you had a great time. Chiang Mai is a great place.

The reason why riding is bad for elephants is there spines aren't built to hold weight on their backs. They can only hold about 300lbs comfortably for a short while before it causes problems for them. The carriages they wear weigh a little over 100 combined with any amount of people starts to cause back problems, and the straps on the carriages rub against their skin and causes injuries.

Good for you for supporting the sanctuaries. There's unfortunately still a lot of elephant riding attractions in Chiang Mai as well, and they're usually chained up and stand around waiting for customers.