You may recall a certain war faught against the British...
A tyranny must be recognized. See: https://en.wikipedia.org/wiki/American_Revolution
"The Continental Congress declared King George a tyrant who trampled the colonists' rights as Englishmen..."
If you recognize a tyranny but do nothing, you stand to receive further oppression. Consider the case of the PRC. The CCP is tyrannical toward those they rule; we plainly see this reality from our perch of liberty. However, unless the Chinese people recognize the tyrannical nature of the CCP, they'll continue receiving oppression. Making this realization harder is the PRC's surveillance apparatus and the population's indoctrination. I wish them luck.
And because they suppressed (non voting, poor) people in the UK didn't declare their king a tyrant it wasn't one for them.
I don't know the exact reasons people put up with tyranny. I suspect every situation is somewhat unique. However, answering that question would allow many future harms to be prevented.
The American revolutionaries declared King George III a tyrant, but that couldn't be the end; open rebellion would mean certain harm or death. So, they acted. They made a case for taking up arms against the crown. They then resolved to become independent (found in the Lee Resolution/"Resolution of Independence"). Two days later, they declared independence. And they fought. Note, though, that the Revolution required the recognition of tyranny.