I would also go as far as to say a Harris is likely the most popular because it's the cheapest of the bipods even worth mentioning. You see it every day at the range or competitions. Shooters have thousands of dollars into their rifles and optics but their ancillary equipment is junk and they wonder why their $5000 rifle is not consistent.
I would say it's the most popular because one can deploy the bipod and extend the leg in a fraction of the time it takes to deploy an Atlas, Sako, LRA...
It is also a robust, dependable and proven bipod that many would and gladly do put under their $5000 rifle and shoot it with consistency.