In this article, Are Legacy Cloud Providers Here to Stay?, we read:

When talking about the legacy cloud providers, the some common names usually come up. Amazon has become the leader in providing cloud services with its Amazon Web Services (AWS), jumping out to a dominant lead in terms of market share at 27 percent. That’s a larger share than its next four closest competitors combined. Microsoft with its Microsoft Azure service is second place with an 8 percent market share, though it is growing at the fastest rate of 154 percent, a much faster rate than AWS. IBM comes in third at 6.5 percent market share and a rate of growth of 80 percent. Combine these tech giants with Google, which is also in the top five, and it forms a clear picture of the level of competition for cloud computing customers.

What is the life-span of such providers? IMHO, quite long -- the incentive for switching from one provider to another is pretty low, assuming the provide meets SLAs. Here is a solid list of infrastructure-as-a-service (IAAS) providers.