It is not unsustainable. For the average fan it is hard to understand how the average spanish person makes something like a million in their entire lifetime. But a football player can cost over 90 mm. It is something that most people cannot understand in the short time they actually spend on football. If you would sit them into a class and give a 2 hour lecture it would be different, but if they only read about it 5 minutes in the newspaper before work a subject as complex as this is hard do digest.
Madrid not only signs a big player each year, their business model requires them to sign a big player each year. They are the biggest club, because they spend the most.
You think people would care about madrid in the last years the way they do if their record transfer would be a player for 10mm ?
Bale did not cost 90mm he cost 90mm - 50mm for oezil. so a 40 mm transfer in total which is a price for a shit load of players today.
The big issue that people dont understand is attention. Its the same way that people cant udnerstand what makes facebook or google so valuable.
We always get the argument that you cant sell jerseys for 90 mm, but madrid sells vip lounges, bed sheets and cups with the logo, all their commerial deals depend on a signing like Bale.
To end this, just think about how many articles or tweets did you read about madrid winning the champions league last year ? one the next mroning? maybe a longer analysis the week after? thats it ! the final is over, the coverage of it is over.
And now ask yourself how many articles you have read about Bale signing with madrid.
Starting with the rumors that he wants to leave tottenham, followed by people discussing what he is worth, followed by the spurs denying a transfer. every day a new update if it is happening or not, then you talk about if the money is too much or not, how a lcub can spend so much.
then you talk about if he is worth his money after he played his first game.
and now you have the constant rumors about him leaving to united or chelsea or even arsenal.
Bale has created more articles, tweets and attention that winning the champions league 3 years in a row could ever do.
He is worth every fucking penny Madrid paid for him.