[oniTony]

> I told them both I'd work for low/no pay remotely to prove myself before I relocate.

Interns get paid more than "low/no pay". I can't know this for sure, but that point might have came across as "desperate for experience" rather than "excited about [company] in specific".

Don't undersell yourself; and as others have pointed out -- build something to show to the founders (prototype, experiment, or just something they would find neat).