Take Google for instance. The biggest hurdles they had to deployment are the protective hurdles put in place by ISP friendly politicians. Some states have regulation in place that new deployments must reach last mile to virtually every resident, which is cost and time prohibitive when there's no profit initially. You have to bite the bullet and do the deployment as necessary, bend to the legal winds and bear the full cost (which, even for Google may be a bit high) with no guarantee of profit until years after deployment.
4G is a bit tricky as well since there are areas where you'll have little choice but to rent existing towers or build your own. In some places, the terrain gets in the way, so towers are fairly limited in what they can do. Then there are the issues with maintenance and safety for crews working on these towers, which cell providers don't seem to care much about http://www.propublica.org/article/cell-tower-fatalities