>It is literally illegal for them to not do what's going to provide the best return to shareholders.

Yes, management famously only takes decisions that are best for the company. All they have to do is pinky swear that they believe they are acting in the best interests of the company.

>nobody is doing a stock buyback to personally enrich themselves.

Well, except for the ones who are.

>Do you think there's a difference between owners and shareholders?

No? God forbid people use synonyms!

>Cashing out means selling shares

No, not necessarily.

>doing a buyback relies on the market to uphold the current valuation and increase the share price to keep the market cap level

So what?

>If the market thinks insiders are only doing the buyback to 'cash out' and that it's not in the best interest of the corporation, that won't happen.

"The market" thinks Bitcoins are worth $16,524 and that Gamestop increased in value more than 50-fold in a few months' time.