Donating money isn't the same thing as providing the actual service. Let's say he wants to give away internet to all of Minneapolis. Honestly we're only serving .001% of the US population...so let's go then with NYC. NYC's population (as of 2013) is 8.406 million. The US population is 318.9 million...so now we're into numbers that we can kind of shrug our shoulders and go "eh a difference was made". Now Manhattan Island itself runs 13.4 miles long and 2.3 miles wide (at its widest). How much cable would have to be laid (or purchased)? Now let's assume you have to run your drops to each household because you're a real philanthropist willing to put your money where your mouth is. I've seen estimates that put the number of buildings on Manhattan Island at around 60000 buildings. Many of those are multi-level buildings, but let's just be snarky and assume we have a magic wifi hotspot that will carry signal to as high of a floor we want with the same latency as CAT 5e. You still have to have techs go out and lay those drops. You'll need switches and routers for provisioning. You'll need staff to configure, setup, and maintain those. You also care about security so you'll need to be applying patches/updates. And you'll want firewalls.Now people are sometimes bad and the courts sometimes needs to knock a few heads in a legal manner for things like child porn or whatever. So you'll need some way to handle subpoenas for records and, of course, you'll need to store those. You'll also need staff to assist in managing the staff of techs, benefits, and vehicles. There's also tools and expendables you'll need to consider.
Are you starting to get a feel for where I'm going? You might have great ROI, but honestly you only pulled back about $350K. Take out taxes and broker fees and you might have enough to handle a few techs. Certainly not their benefits nor the managing staff's benefits. We haven't even gotten to things like software licensing, legal paperwork/attorney fees, and other administrative costs. Also there's the value of your own time to consider.
Giving away money is far easier than actually building/running an organization. To suggest a single digit billionaire has the capital to do this is ludicrous. As an example just Verizon's wire-line business pulled in 15.6 billion in 2014. That was a small amount of Verizon's total revenue of $157 billion. Of that only $9.625 billion remained as net income. It is simply not possible for an individual to give away free internet to any chunk of the population larger than maybe 1/4 of a percent.