Except it's not - for 200/20 at those prices the GP must be talking about a Virgin Media line, and they run their own cables. The increased competition between providers probably contributes to driving down prices to just above the point of profitability, but its not responsible for the infrastructure in this case.

200/20 is available from Openreach as fibre-to-the-premises but it's rare and only a handful of providers offer it.

I think the common base-level infrastructure helped drive ISPs to compete on service & feature + meant they can use their funds to implement those features.