She won the throne (in every way except actually sitting in the chair) and THEN killed seemingly everyone in the city. 500,000 to a million people. The common people.

As Jorah told her "The common people pray for rain, health, and a summer that never ends. They don't care what games the high lords play."

And the high lords? They're on her side. They told her in the previous episode that Dorne was with her, the Iron Islands are with her, The King in the North supports her. She already decimated the Reach. They faced her Dragons and saw what happens. She already took Casterly Rock, the seat of the Westerlands and she already took the Stormlands. (We don't really know what's going on in The Vale or The Riverlands at this point.)

The high lords of Westeros already knows what happens if you defy her. So, the point of killing the common people in King's Landing? Because they didn't "rise up and overthrow Cersei" (who it was established through action and dialogue that they hate)?