Back a while ago before I got global entry, I was doing 2-3 entries per month over a 3 month period using visa waiver on my UK passport... I got a comment from an immigration officers one of those times, saying that I come so often, I should get a normal business visa... I just smiled and said maybe I should, and that was the end of that.. Pretty sure the officers would take note of it or systems might flag you for some additional questions.... but if you have a valid reason, they probably wouldn't bother you too much about your frequent travel...