I'd rather each bank do the due diligence themselves than some centralized entity removed from anything.

Also almost all the things GP listed apply all across Europe. So the "Spain character assassination" exercise is pointless.

Well you're in luck because almost all US residential mortgage lenders perform that due diligence. Credit scores may be a factor in determining loan approval and interest rate but they also look at other metrics including DTI, LTV, and others.

Then what's the point of centralized scoring agencies except for selling your data?

Those aren't really "scoring agencies". The credit reporting agencies make most of their money with mortgage lenders by selling high-quality data. Credit scores are more of an add-on, and mainly of interest to other types of lenders dealing with smaller loans who can't afford to do rigorous underwriting themselves.