Cloud computing is a model of renting resources - servers and data storage. Both servers and data storage have been around for much more than a decade so far. Yet cloud computing offers only appeared several years ago.

What's the deal here? What was the critical change that triggered massive adoption and massive marketing of cloud computing offers?

It has appeared earlier. In fact, this was the original model of getting access to computing resources back in the 1950s till well into the 1980s, when it was called "time sharing", then in the early 1990s it re-appeared under the name "Client/Server", then in the late 1990s again under the name "Thin Client", then "Application Service Provider".

However, in the exact form we see it today it requires high quality, high reliability, high throughput, low latency, low price, ubiquitous Internet access, which didn't exist until a few years ago, and in fact, still doesn't exist for the vast majority of people (e.g. almost all of Africa, much of Asia, parts of Eastern Europe and South America).
