Verbal Offer Reneged

Hi y'all, after a very lengthy interview process (10 interviews), I had a verbal offer from a large commodity trading house for a junior role. This was communicated to me by a recruiter ("Xx has asked me to make you an offer"). After we discussed comps, I didn't hear back until a month later when the recruiter informed me they are moving ahead with another candidate. During which time, I chased him consistently asking for updates.What could have happened here? I do note I'm an expensive hire compared to others applying for the same position, coming from a big bank in the commodities space. Also inconvenient as would require visa sponsorship. But neither of these should be prohibitive for them considering their record profit year. Should I contact HR directly or maybe the people who interviewed me? What is the etiquette when you were referred by a recruiter?