The argument is the same as applied to governance, you don't want to give one person or entity too much power.
I find the crusade against Google ridiculous for the most part, they're one of the few entities who are doing actual, quantifiable good in this world whilst demanding surprisingly little of me. Compare with for instance Facebook which is really just Zuckerberg's boyish stalker-fetish turned billion-dollar industry.
The flip side of spreading your data across several providers is that you are increasing the odds of finding a problem. But the problem will have a smaller impact (hopefully).
But you're not actually splitting your data across several providers, in many cases, you're making copies of the same data, and so you're actually increasing your exposure.
I find the crusade against Google ridiculous for the most part, they're one of the few entities who are doing actual, quantifiable good in this world whilst demanding surprisingly little of me. Compare with for instance Facebook which is really just Zuckerberg's boyish stalker-fetish turned billion-dollar industry.