It’s only a few countries where rampant corruption is the exception and not the rule — the US is one such country but many Americans don’t recognize this because they have no comparison reference.
There are specific laws restricting/regulating people who go from government to industry, intended to address conflicts of interest.
You are repeating a cliche that wrongly makes it sound like nobody ever thought of the issue.
The problem with casual cynicism based on ignorance is that it allows you to fall right into the trap of trusting corrupt people who say everybody else is the same.
Do you think that if a few powerful people do get treated differently, that means the system is totally corrupt regardless of whether ordinary people have constraints and generally do what they should?
* https://risk-indexes.com/global-corruption-index/
* https://www.transparency.org/en/cpi/2020/index/usa
The US has its problems, God knows. But you've never seen real corruption if you think it's anywhere close to the worst.
That's just some institution at a conference not wanting to be pestered, which is something else entirely.