I really find Corporate Speak annoying as hell. How could anyone read this and take it seriously? ..."Here at Dropbox.. We earn your trust...". The whole "Here at $X" is the most annoying part.
I'll speak to risk first.
If you are a company delivering a report to shareholders, the risk is primarily downside risk. It's unlikely for your stock to skyrocket if you say something clever, but it might fall if you spook them. This is because the default assumption for companies is that management is already competent, so the risk distribution has more downside than upside. I see corporate speak as a tool to avoid spooking folks and triggering this downside risk. (Notably, there is a positive feedback loop, where non-corporate speak becomes a stronger signal as it becomes rarer.)
On the other hand, if you are a startup company trying to break into a market, the risk is primarily upside risk -- if your communications go well, your business could eventually grow by many multiples. And achieving growth almost always means differentiating yourself from competitors. The reason that many startups eschew corporate speak is not necessarily because they are smarter, but simply because they are adapted to their environment. Avoiding corporate speak is the correct strategy when your upside risk is high.
The second issue is scale. It applies to both the receivers of the messaging and the senders of the messaging.
If you are selling to a specific niche, you can use the language and sensibilities of that niche when crafting your message. But if you are selling to a broad base composed of many niches, this customization of language is no longer possible. Anything too non-standard risks distancing certain niches. This is why when you are selling to a large audience, your communication necessarily needs to be blander than if you are a selling to a specific niche.
Another force that pushes corporate speak is coherence. When you have one voice, as individuals or startups might, it's easy to keep messaging consistent and coherent. Avoiding mistakes is easier, because there's only one point of failure. But as your company scales, you suddenly have hundreds of people putting out communications (and there is constant turnover among these folks). In this setting, it's hard to keep the style of these communications unique and consist. It's also harder to prevent dumb mistakes, since there are now hundreds of points of failure. Relative to more personal or unique styles, corporate speak is easier to apply across large organizations.
Lastly, and relatedly, I think corporate speak often arises as a result of people optimizing individually. If I'm putting out communications, I could get fired if someone doesn't like my bold/honest/creative take. But if I put out something bland, especially in an environment while others are putting out something bland, I'm not going to get fired. It's a similar risk argument as above, but applied to people. If I write a great a blog post for my company, no one is going to double my salary. But if I write a disastrous blog post for my company, I'm getting canned. The risk is asymmetric.
I think you nailed it.