Perhaps the founders believed their product would go further (not die) under Amazon or that they stood to benefit more from stock rewards long term
If the shareholders were not part of a vote, ie. the board voted, then the board is potentially liable for damages.
Otherwise one state would have a monopoly based on it being business friendl... oh wait, maybe that is the case.
The corporate charter, and the bylaws of the corporation are all explicitly governed by Delaware law. These documents control what powers different share classes have regarding corporate ownership and operation.
TLDR: Delaware law is almost certainly the controlling law regardless of where the shareholder lives.
What's often misunderstood is what "fiduciary duty" means. It doesn't mean "make the most amount of money possible", it means "act in the best interest of".
In a cash acquisition, no. There aren't. The owners have no continuing consideration.
If the acquirer wants post-acquisition concerns to weigh on pre-acquisiton shareholders, their offer should include a stock component.
The problem is the 'shareholders' is made of multiple groups.
A relatively common setup is Investors, Founders, Other Common Share Holders (Employees, Gifts). If there are 10 seats, Other Common will likely only hold 1 vote.
So the board voted in its best fiduciary duty that represents 90% of the votes. It's quite easy to see how employees can get the raw end of the stick.
Shareholders can indeed vote however they want.
Board members are fiduciaries, and vote on behalf of all shareholders. That a board member is also a shareholder (say, the founder) doesn't remove her duties to all shareholders.
While fiduciary duties are somewhat broad & fuzzy most of the time, they narrow during a sale of a company to basically "get the most money". These are "Revlon duties", after https://en.m.wikipedia.org/wiki/Revlon,_Inc._v._MacAndrews_%....