Also, sending a singal across fiber is definitely not easy.

ADSL is basically modulating a radio wave over a cable directly to another device. Fiber requires high quality optics, high quality lasers, tons of active hardware if you want to do it at scale. (not to mention the mind boggling physics and manufacturing required for things like DWDM, optical path switching etc).

Fiber optics have existed since the 80's yes, but prices of high quality fiber solutions have only dropped massively in the last decade or so.

Don't go for GPON, if you have a chance. Direct cabinet-to-apartment single-mode fiber (can be a pair that gets BiDi optics if one of the fibers fails, though only worth it if correlated failures aren't the bulk of issues) is future-proof. Also GPON tends to not get anywhere near the awesome pings 1G-LR and 10G-LR provide in sub-lightpseed regional situations.