That's most likely the answer. I've been an expat from down the equator for more than 15 years and most US companies will not bother offering sponsorships for someone without some seniority already. Europe is more accepting regarding this.
Your resume could use some polishing, but I don't think that this is the problem at all.
try looking for internships in Europe, they're a lot better at getting foreigners in as Interns. Germany especially, and since you have experience there before it may not be a bad idea. There are several good startups in Berlin looking for people with your skillset. Leave a comment if you're interested and I'll drop you a mail with some leads in Berlin.
Yeah for sure I'm interested. That would be great, Thank you!
Facebook has a large Engineering office in London these days and we take interns.