If it's the 90% figure you doubt, I encourage you to look into some road projects. In Virginia, we have a particularly problematic system where the local contribution is pegged at 2% (see page 52)(though it can vary by project.) You are welcome to read the VA urban (misnomer) maintenance code, though I encourage you to find the one applicable to you, so you can be familiar with the perverse incentives provided in your own area. [http://www.virginiadot.org/business/resources/local_assistan...]
Reality is that more people now live in urban areas[1]. Democracy being what it is, most funding goes to the majority - which are in the city. Add to that that setting up this infrastructure is often not cost effective for a private business (due to a lack of customers) and that most rural communities prefer less government intervention (ie less taxes), we have a situation where there is little impetus to invest in rural communities by private companies and governments (at least local) don't have funding to pay for service.
[1] https://www.census.gov/library/visualizations/2016/comm/acs-...
Democracy has to be more than two wolves and a sheep deciding what's for dinner.
It's true that the majority can just vote to line their own pockets and leave the minority in squalor, but that leaves a pretty shitty country leftover. Many of these rural areas look like third-world countries and that's not something us urbanites should be proud of.
Scholarship money disproportionately goes to lower income students, but that doesn't mean we should stop giving them scholarship money.
https://en.m.wikipedia.org/wiki/Urbanization_in_the_United_S...
Yes. Society should always be doing more than what is cost optimal.
Cities are only being focused on right now naturally because that's where the rich people are. It wasn't that long ago that inner cities were quite poor and there were people making excuses like you for not investing in them.