No matter who it is, how long it has been around, or what the service is... if it is a cloud service it will one day go away.
Actually, it's not just the cloud, it's Real Life(tm) too.
That coffeeshop you buy your java brew from may decide one day to stop serving it at all. Or it may close up shop. Or it may change owners and molest the brew to something vile and undrinkable.
The Cloud is not much different than anything else. Your favorite store might change hands, close down, stop offering the goods you want, etc.
Anything you buy from others is subject to shutdown. While unlikely, your ISP might decide to close up shop and stop providing internet service to you. Or your colo provider may not be able to renew its lease and have to shut down.
Yes, some of these companies have been around a long time, but remember they're survivors - thousands of other companies have came and went.
The oldest company in North America is the Hudson Bay Company (now a Canadian department store, formerly a fur trading business). Doesn't mean it'll be around tomorrow, and for every company that's been in business for 340+ years, millions of others have been started, closed and so forth.
Cloud companies are just the same - another service that can be here today, gone tomorrow.