I don't believe we are talking about stock market investing here, and "unexpected market changes" don't happen in a vacuum, but are driven by the customers' preferences.
Who's speaking about stock market? Those companies didn't exist in a vacuum or in Wall Street only - they had customers which were hit by the bankruptcies and may have lost a lot.
"Unexpected market changes" are not only driven by customers, but also by the appearance of new technologies the incumbents could not grasp in time. There could be also ill decisions and many other situations that can run a successful company into the ground. Splits, spin-offs of less remunerative branches of business, and merger happens, and companies do realign their priorities.
if they hold all of your data, I'd be very careful about having all one's eggs in a basket. You like to talk about the stock market, do you put all of your money into a single investment because you trust a company so much? Or do you fear it could crash one day? There's a reason why banks in most parts of the world are heavily regulated and customers' money partly protected by governments... maybe one day that will happen to data also, but not now.
Thinking that cloud storage and applications will be there "for ever" is quite dangerous - and especially if you are one of the smallest customers you are among the ones more at risk - as you are an irrelevant percentage of their profit (if even a profit).