This is a deep misunderstanding of human psychology.

> the top of the company should love because a) you saved them a ton of money

The top of the company is probably already rich. Being richer is great, but one of the few things rich people generally won't burn to run the money-making engine hotter is their own sense of prestige and entitlement.

> b) you identified a pile of incompetence in their company.

Yes, and you told that fact to people who were already responsible for identifying that, which means you just told them that they are incompetent too. And that transitively works its way all the way up the org chart.

You would make the whole chain of command lose face and do so in front of the rest of the chain of command. It would be career suicide.

Every manager would rather silently waste money than be made to look like a fool. Because the money comes out of the business's bank account, not theirs, but looking stupid affects their personal reputation.

That sounds like a very nice and theatrical outcome, but in reality nobody wants to believe they've been horribly wrong about their understanding of things, which means the higher-ups are going to be talking directly to the managers to get their side and figure out how they can show you've misrepresented the situation. They're not going to fire managers en masse because the new guy said "Everyone here is dumb and cowardly," even with evidence.

this assumes that the "top of the company" is a shining tower of competence, blissfully unaware of how incompetent the people below them are.

more likely, the top of the company is just as incompetent but has lucked / gamed their way into promotions anyways.

So this engineer throwing his managers under the bus may be good for the company in theory, but to the senior management this is a red flag. they don't want engineers who do this - they want engineers who give credit to their managers. if they promoted this engineer and fired everyone else, he'd come for them next.

It would, I replied to someone else below to explain why. But in general, it's best for your future career to be remembered well.

The thing about burning bridges is you don't know when you'll need them.

Let's say 5 or 10 years later you're applying to a job where one of these upper-level people now work. How do you want them to remember you? The know-it-all who wasn't a team player and kind of an asshole? Or the engineer who gets things done and has demonstrably shown to land impact and value, an engineer the exec would consider lucky to have?

Some of you will say you wouldn't want to work for one of these executives again. But people change, incentives change, the environment changes. Have you ever made a technical decision you later regretted?

And maybe you don't work for them. Maybe you're applying to a different company where someone knows these previous upper-level management folks and they ask about you. How do you want that recommendation to come across? "That engineer was an asshole.", "That engineer was amazing, I wish we could have kept them. We made a big mistake by not trying to keep them.".

Tech is a small circle. Unless it's something obviously wrong, you may want to be at least milder :)