The accent is much stronger depending on how close you grew up to the city itself. It also tends to fade out over time but I know some adults that still have a pretty thick accent. In Pittsburgh, we call them "Yinzers". The only ones that definitely should have had the accent in the movie would have been Jeb and his goons and Sandy. She was the perfect Yinzer. I can definitely buy the attorney, her father, and the detectives not having a stereotypical Pittsburgh accent as they likely didn't grow up in the city itself. What would have been really funny is if someone asked Reacher for a gum-band (rubber band) or what kind of pop (soda) he wanted. That's way more common in Western Pa than the Yinzer accent.

Yinz/YunsYou'ins (think the Pennsylvanian way of saying Y'all)
Listen to themthe children of the night. What music they make!

My mom is from Philly but what does " yuns" mean? Like how would you use it in a sentence if you don't mind?

You idiot !!!! The shooting is outside the damn pnc stadium !!!!!!
And the range that he drives to is in Ohio !

In the scene where they are explaining about the construction company, the paperwork for the company's sale, which the owner's widow doesn't sign actually says Pittsburgh.
That's the only way I knew what the heck city it was set in.

it was definitely in Pitt pretty sure there was even a shot of the PNC park. ROTHLISBERGER HUCKEM CHUCKEM FOOTBALL

It ABSOLUTELY was set in Pittsburgh. The plot synopsis says so, and the use of obvious land marks and the riverfront confirms it. Not to mention the Pirates hat.

What are you talking about?

The story's set in Indiana
Fighting a religious war is like fighting over whose imaginary friend is better.

Correct. You can find the accent in areas far from the city.
And there's definitely an accent. It might not seem like it to a lot of people, but it's there. used to think it wasn't very widespread but when I first moved to L.A., I had more than a few people comment on it.
It just isn't as extreme as people tend to claim.
And it's "yinz", not "yuns".
You guys just made me homesick.

The accents don't disappear when you get out of the city limits.
The movie was set in western Pennsylvania. The Pittsburgh accent is common in all of western PA, Northern WV, and eastern Ohio.

It was filmed in Pittsburgh, not set there.
Fighting a religious war is like fighting over whose imaginary friend is better.