The last time we discussed the topic of which pokestop gets promoted to a gym is linked here:From PokeStop to Gym?
Staff did not weigh in on that post. From the even older link I quoted there, I would have to agree with the assessment that Niantic “intends” the process to be random, even though it has been observed to be able to be influenced in the past. This may have happened in this case if those gyms are all older Wayspots.