Because I've had problems with it for a few weeks. I can open the front page, then maybe a few other pages if I'm lucky, and then everything just stops, and I can't access anything on the site for a while. It's not a browser issue - hell, it's not even a computer issue, since even my Wii U is affected. And it's just Serebii's main site itself, even the forums run fine, along with literally every website I visit. One of my old regulars reports having the same problem, but another one has no issues whatsoever.
So if you have a few seconds to waste, could you please test it out on your end? The best way to figure out quickly whether there are problems, in my experience, is to open a bunch of news pages and see if they all load, images and all.