Broadband infrastructure investments have a positive impact on more elements of society than captured by the traditional return on investment calculation you are making. You’ll need to also consider the positive social and economic benefits of the project. As noted in the article for example, tech companies "will hire at least 215 new employees within the next five years with completion of the expanded network… total payroll from those jobs would be $12 million”. Other considerations include things like acceleration of innovation, increased productivity, and attracting employment from other regions which increases the tax base. For these reasons this infrastructure project is different from the others cited in your post.