Too bad the government doesn't want "cheap energy". They want something they can tax and control. Also, if you make a highway out of this, it will create a lot of electricity one day and can create very little the next due to traffic that day. Yes, it is an EXTREMELY FANTASTIC idea! But, the government probably wants nothing to do with it on the larger scale uses.
It also steals energy from you walking on it, but it still wouldn't be as bad as say, walking through loose sand on the beach. More like constantly walking up a very slight uphill grade.
Also, I bet these tiles cost somewhere in the tens of thousands of dollars each. No green projects are ever cheap. If green were cheaper than fossil fuels, they wouldn't have to subsidize it. So I wouldn't call this "cheap energy" that the government doesn't want. I'd call it really expensive energy that is impractical to implement on a large scale because of the initial and inevitable ongoing maintenance costs.