It is the only metric of measurable success other than feelycraft that is why it is being used. It represents people putting considerable time and effort into blu, something the other trackable stats to not.
But if we are taking feelycraft here, just look at any of the blu content discords, they were saying its been hard to find groups since week 2 of release, youll get 1 or maybe 2 posts looking for groups daily that take a while to fill. Pfs stay up for upwards of an hour just for skills, let alone blu log runs which take an age to fill if they fill at all. But thats all subjective feelycraft which other people can dispute with their own subjective experience (or fibs). This is why people try to use data.
Edit: btw, I am very much in the camp of loves blue mage but wont do morbol mount btw. And therin lies the issue. I find playing as and being a blue mage fun, yet one needs to jump through hoops and do years old content to get that fun. For someone like me there is nothing to do on BLU, i have no desire to run old content again sync'd and ive already done what the masked carnival had to offer me in less than an hour. So here I am, stuck with a class that I enjoy and nothing to enjoy it with (other than rarely helping my friends level)