“Call a SPADE, a SPADE; and a TRANNY, a TRANNY, or an IT!!!”.
"THAT'S SOME BAD
SHIT
,
HARRY
!".

What's the reason why most people retire?
Actors are no different but I think we expect them to be. It's the one profession that we anticipate someone will continue to do until they die or is physically unablewhichever comes first.
Why? I guess it's because "art imitates life" and "life imitates art". So, as long as there is a story to be told, we have the need to see actors working way past the age of retirement because life goes on. And, especially if an actor continues to possess exceptional talent and screen presence, we don't ever want to say goodbye.
Out of respect and admiration to Mr. Gene Hackman. I'm simply going to sayThank You! For your numerous films, years of service and quality of work. I enjoyed watching.

He just got tired of all the rigmarole that goes with it. Also he wanted to focus on his writing (he writes historical fiction).
The further a society drifts from the truth, the more it will hate those that speak it.

did he gave a statement or a reason

Where have you been, under a rock?
He
retired
in 2004.