The interesting thing about FTTH is that it's not all created equal. You probably understand this from your comment. Many don't.
In a passively split FTTH deployment, the one fiber going back to the ISP's switch may be a 1 Gbps port, but it is passively split amongst however many subscribers they've decided upon, 1, 4, 8, 16, 32, 64, etc. So just because an ISP runs fiber to your premise, doesn't mean it is able to support 1 Gpbs.
Then again, most ISP's will tell you that nobody even wants anything more than 3 Mbps, otherwise they'd offer it.