"100/20 is barely enough for a household of 3-5 "light" users."
It's plenty for my household with a similar number of users. We have people working from home, streaming, downloading documents or games, etc with no problem.
"The US already has abysmal broadband speed/bandwidth/latency metrics compared to the rest of the developed world"
Because the countries in the rest of the developed world are about the size of 1 state and have higher urbanization. If you want better coverage for an area this size, then it makes sense to include satellite coverage. The gigabit goal excludes them.
"Why spend money and time to expand copper into rural areas when fiber is the same cost."
They're only the same cost if you're starting from the same location. Copper has better penentration already. Expanding copper might mean adding a couple miles. Expanding to that same location with copper might mean putting in 10-50 miles plus any sort of hub or substation. So yes, equal distance is roughly equal cost, but almost everywhere fiber is put in, it's alongside copper anad thus not increasing coverage nor decreasing costs.