The only thing anyone seems to say is 'because it's Madrid'. By that rationale their whole team is available and could be linked to us. Madrid won't let Bale go yet.
They are, more or less. Only a handful of them are considered indispensable.
Why Bale?
He's expensive - he's the second highest paid in the squad, a salary justified by Perez because he's "a future Ballon D'Or" which barring an amazing turnround he isn't.
Madrid determine transfer fees in two parts: the player + the marketing. In Bale's case the expected marketing advantage didn't work out. He was supposed to replace Beckham in the English speaking world, his photo on the billboards for the PL seemed to say he'd made it, they liked the heart thing and the Adidas sponsorship. But he just isn't that sort of PR hit. They overpaid by their criteria, if they can turn in a profit they'll be tempted.
They are looking at Reus at €25m. But they are also looking at Jese who's from their own academy (they are desperate for one of their own to make it) and Isco, who might give them as much in front of goal, but potentially given them more in patient build-up and in possession play. If Bale is not impossible to sell then it could be a matter of cash.
The real question of course is what does Bale think about it. He's got a contract that runs until 2019, a big salary, a role in what looks like it's going to be a very successful team. What's in it for him? I've not heard many rumours about homesickness or about him feeling marginalised. I don't know why we would think that he would want to come, but I can see why we might believe he's available.