Milk kefir starters are a little more prevalent, but the kefir starters can only be used for a short time before they lose their potency, whereas kefir milk grains can be saved and used for many lifetimes, being passed down for generations. Kefir grains are meant to be shared.
Like many cultural dietary inclusions and medicines, kefir is a functional beverage that is only just becoming more widely known in North America. North America is a new 'culture' that seems to have (in many instances) lost touch with ancestral roots. Many things; folk lore, knowledge of natural cures, recipes, and healthy foods to name a few, are no longer shared. Before the internet, the knowledge of such things was lost in the new world.
I find that the farther west you go in North America, the more likely you are to find alternative medicine and food practices. I think there are many reasons for this, but mainly Western Canada and U.S. is both more densely populated and much more culturally diverse. Also the western shore is closer to Asia where alternative health is part of their culture!
Thanks to the internet, a local economy is becoming more global. Knowledge of different cultures is available in most homes now, and people who wish to learn about the healthy traditions of long lost ancestors can easily find that information.
Once I had the knowledge of the health benefits of milk kefir, and the experience of making milk kefir from grains, I felt it my duty to make available the milk kefir grains. Canada is not so entrenched in their own culture that there is no room for something so delicious and beneficial to health. Milk Kefir IS a part of our everybody's ancestral heritage if we go back far enough.