The 'issue' described is not just confined to Ryanair.
Most airline reservation systems are programmed with complicated algorithms to 'respond' to customer demands, enquiries and booking patterns.
So.... essentially - the more 'in demand' seats are, or appear to be, the higher the price will rise. The more that available seats are 'ignored', the more the price will fall in order to attract business at that price point or during that travel period. In addition - prices available on different markets may also vary according to demand from or to that market.
Simple and very effective.