It's not just Ryanair, United for example has the following policy:
The use of still and video cameras, film or digital, including any cellular or other devices that have this capability, is permitted only for recording of personal events. However, photography, audio, or video recording of other customers without their express prior consent is strictly prohibited. Also, unauthorized photography, audio, or video recording of airline personnel, aircraft equipment, or procedures is always prohibited. Any voice, audio, video, or other photography (motion or still), recording, or transmission while on any United Airlines aircraft is strictly prohibited, except to the extent specifically permitted by United Airlines.