It is not just the weakness of Sterling but a general lack of confidence in global markets. In addition Spanish property became grossly over priced in the property boom. Far to much property of a certain shoddy type was built on illusions of never ending demand.
There is also huge disillusionment in the Spanish system due to corruption and a lack of concerted action by the government to help people when things go wrong. In addition the costs to buy, sell and maintain a holiday home make no sense.
Few people now believe Spain is a desirable destination for retirement or even a holiday. There are more attractive destinations within financial reach around the world.
In short Spain is clapped out, over developed and had it’s day.