In some cases even more than costly to build, they're an area of cutting edge research. The public assume that it's just a matter of building a "big wire", but

In some cases even more than costly to build, they're an area of cutting edge research. The public assume that it's just a matter of building a "big wire", but the "big" here has to be so big to be effective that we're actually into the realm of new materials science. The idea of solar panels in Africa powering homes in Europe is probably unlikely to happen for a long time, and even if it did history has shown us time and again that a distributed network is far more resilient than a centralised one, and so the best solutions look a lot more like putting solar panels on every house.