The U.S. government incentivised the creation of the transcontinental railroad by paying the railroad builders $16,000 per mile of finished track.
That's the right way to build home broadband networks too.
For example when an ISP proves that it has installed a broadband connection of a certain speed into a home, then the ISP should be paid $16,000 (substitute this for the appropriate incentive amount).
You get the outcomes you reward. If governments want fast home broadband then that's what they should pay for.