The Monica incident is the reason, yes.
It started at the 1993 Wimbledon, I believe in direct response to the Seles stabbing. Given how open access to the courts are from the stands (eg the streakers and protesters this week), they were very concerned about having players sat with their back exposed to a significant section of the crowd mere feet away.
So they changed the chairs. But a lot of players don't like it, and change them to the standard configuration.