Disclosure: I've been working with Tutum since the initial team.

Tutum was actually a container hosting service at first but we found there were a ton of technical challenges in multi-tenancy with hundreds/thousands of containers and it's hard to build a level of trust that larger IaaS providers have like AWS.

Hosting puts you in direct competition with IaaS providers, while being a middle-man can provide more value-add and you get to work with the other providers to strengthen your solution.