Why do people follow bandwagen teams?

It really pisses me off considering all the bandwagen teams are in spain and I'm spanish. I went to the usa and spain game and i saw a bunch of Americans with spain shirts rooting for them and everyones favorite team is barca or real madrid. Why can't people support teams like tottenham or kashima antlers? I have more national pride in japan even though I'm not japanese than spain where I'm from.