Why didn't Michael Keaton just offer suggestions to the script if he thought that it sucked?

That's his own words for why he didn't play Batman for a third time.

https://ew.com/movies/2017/01/04/michael-keaton-turned-down-batman-forever-because-the-script-sucked/#:~:text=During%20a%20new%20interview%20with,The%20script%20never%20was%20great.

https://www.indiewire.com/2017/01/michael-keaton-passed-on-batman-forever-the-script-sucked-interview-1201764509/

I would figure that after two Batman movies under his belt, he had enough industry cred to offer suggestions to Joel Schumacher or any other Batman film director.