It's a Ryanair feature. In the days of open seating Ryanair used to close off seats at front and rear, dependent on the booked load (but none closed if a full load), effectively balanced either side of the W&B midpoint, so that they could ensure without further thought that they were within their limits. Everyone was sat scrunched in the centre with empty rows at the outer ends. Tough, you're on Ryanair. It was a crude centre-imposed approach in Ryanair style to ensure being within limits without anyone in the crew having anything to think about.
I believe they had actually had a W&B issue with a half load and all the pax choosing to sit at one end, which some regulator (possibly the IAA) had picked up. A normal operator would have the flight crew check the distribution when all seated and possibly get the cabin crew to redistribute if it looked wrong. FR take a different approach.
Nowadays there are allocated seats, but still a need to avoid any asymmetric distribution, so the various "excuses" handle this.