Keeping Up with Competitors
From a fixed line view, these competitors are pushing for subscribers being able to access content in any device (i.e., smartphones, tablets, PCs, TVs, cars?). Of course the service provider will love to upsell an alternate access medium to customers. While DISH is a capable satellite provider, it has little experience in the terrestrial side. A national buildout of their MSS spectrum would be capital intensive and outside of their core competency.
Enter Sprint
Sprint's big bet in their 2010 Network Vision strategy that hosting spectrum would be an element of its wholesale strategy. There was much promise as then cable company (SpectrumCo) partners had a near national AWS footprint and Clearwire needed a platform to expand to new markets. So far, only the nearly defunct LightSquared was the only shortlived spectrum hosting deal. Therefore, any spectrum holder who needed to bring up service is fair wholesale game. With the Softbank cash infusion, Sprint has publicly stated that it has the flexibility to do more things. Aggressively courting DISH and hosting MSS spectrum should be a no-brainer despite any previous tension on MSS spectrum interference with with Sprint PCS operation.
Possibilities
It's an inevitability that MSS will run LTE. If MSS bands were to increase Sprint's LTE capability beyond their 5X5 channel implementation, a wider LTE band helps Sprint LTE capacity allowing Sprint's Unlimited data proposition to extend. Speed is another factor in which channels can be aggregated to provide a fatter LTE pipe.
A DISH deal allows for a long term alternative (and a lever) to being locked in with Clearwire's TD-LTE. At a minimum, a DISH+Sprint PCS/MSS LTE pipe complements any data offload.