This is one of those ideas that sound great on first glance but aren't when you take a deeper look. The floor absorbs the kinetic energy that a normal floor would normally send back to the spring system that constitutes your foot, making it necessary for you to expend more energy to compensate for it, and that makes walking more tiring. Essentially, the power is created by making it harder to walk. The additional effort that is placed on the people walking is turned into energy at a very low conversion rate. The energy required to create and maintain this machine dwarfs the expected output.