1. There are a host of requirements needed to get the blue check: https://help.twitter.com/en/managing-your-account/about-twit...
2. However, once an account gets the blue check, the owner is free to change the profile pic and display name, and the blue check doesn't go away.
3. So the scam is that some bad guy buys a previously verified account, changes the profile pic and display name to someone else famous, then uses it to phish.
#2 is colossally stupid, and is trivial to prevent (lots of dating sites require profile changes and pic changes to be reviewed before going live). Apparently this has been going on a long time so is baffling to me.