Because Spanish bankruptcy laws are anachronistic in that it kind of does not exist. If your business fails in Spain you are on the hook for entire amount. People have committed suicide over it. There was a movement to get it changed after the GFC 2008 but I'm not sure if they've been brought up to date or not.

Less risky to create a Delaware LLC, open a spanish subdivision, and if it fails no one has to sell their house.

One reason may be to make it easier to raise money. Most VCs know the ins and outs of corporate law (and corporate law precedents!) in Delaware, making signing a contract there a lot easier, as opposed to learning the specificities of Spanish law.

I see. Thanks