Let us not only look at Ryanair in this discussion about contractors.
Most other large corporations use them at will, even Jaguar/Land Rover for their Engineering Department, Lafarge/Tarmac for their motorway maintenance IT and engineering departments, to name just a few...
Several countries allow so called self employed contractors up to a limited amount of years before law requires them to be taken on as employees. Even National Tax Offices use these practices and relieve staff of their requirements and duties weeks before that term expires, only to rehire them a month or so later for another such duration as a contractor...
Ryanair is not alone in this practice as not was Sports Direct, nor the National Tax Office of NL, and many many more. It is a way of employers to release some burden and enable more capacity when needed and assess multiple potential employees for the best suitable candidates to be hired for long term or just temporarily.
Unfortunately many companies abuse the system they've been given, thus this loophole needs to be closed by creating rules as to when these contractors can be used and after which time permanent employment must be offered...