Yes and no. They (or anybody else) are not guaranteed to be secure, of course; see all the compromises regularly found in cloud providers; Azure especially has had so many cross-tenant vulnerabilities (there’s one on the front page right now!) that I’m amazed the concept of public multi-tenant clouds still exists.
But they are also very highly incentivized to be more secure. They have millions of customers (hence a correspondingly higher expectation of trust) and billions in revenue from the trillions in economic activity happening on those platforms (hence a correspondingly larger target on their backs.) This means exponentially higher liabilities. And that probably matters more than any other factor.
But they are also very highly incentivized to be more secure. They have millions of customers (hence a correspondingly higher expectation of trust) and billions in revenue from the trillions in economic activity happening on those platforms (hence a correspondingly larger target on their backs.) This means exponentially higher liabilities. And that probably matters more than any other factor.