What you're talking about is called Unbundled Access / Bitstream access [1]. Although that's currently mostly talked about in the context of copper/DSL access.
The fiber cable itself is enough a commodity that it can be structured (from a business perspective) more like roads or water lines.
This is actually how ISP’s worked at the dawn of home Internet in the US. There’s no way the incumbent monopolies would have given people access to raw TCP/IP if not for decentralized competition. (Look at Prodigy, AOL and Compuserve’s behavior for the decade prior for hard evidence). Historically, the phone company in the US could even block the usage of answering machines and modems. It took anti-trust action to eliminate those bans. We see the same thing today, with AT&T’s crappy FTTN routers, intentional cable modem buffer bloating, and the abomination that is IPTV cable service.
Last mile only competition eliminates all those things.