Hi Laura,
I'm thinking it comes from such things as junior high, high school and college. If I'm not mistaking, when I was a kid, 5/7/5 was the only thing being taught (I'm 63 now!). I think it's a tiny bit earth shattering to some when they find out that there is a different take on it. Folks like to stand up for what they've been taught and believe. It's only natural. That's probably where the passion comes from.
For me, I never really cared. Once I got up to speed that there "is a new count in town", I just said, "whatever" and went with it. LOL
It's going to take more time and work to get the educational system involved enough to learn and accept newer information regarding the differing aspects of the Japanese and English languages, comparatively
Just a tip of the iceberg two cents worth of mine.

all the best,
Don
ps... of course, they may be very experienced and just write it that way because they want to... it's all good!