It's not just maintenance. The system as a whole was architected to take advantage of the economies of scale you get when you assume that your customers remain consumers and you control the production. Nobody foresaw back then that each house could be a potential power plant. When you start to change that, you're still having to maintain the current infrastructure, which is steadily becoming obsolete, while also building new infrastructure to handle random power spikes and draws in arbitrary locations. You have to do this across the whole grid, everywhere in the country. This has the utilities very very nervous.
