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.