Honestly, I don’t remember Romney getting huge crowds. I remember a story about his staff cordoning off half a stadium in Detroit to make it look more full. Maybe he did get huge crowds and I missed it.
But Hillary’s level of support has been comically low - not just crowds. I personally do not know a single Hillary supporter...and all my old lib classmates are all about Bernie. IIRC some of the primaries featured precincts with 100 plus percent voter paparticipation....
I remember Romney getting larger crowds than obama.
Romney had a rally in Apoka Florida that had like 25,000 people. http://www.orlandosentinel.com/news/politics/os-pictures-mitt-romney-rallies-in-apopka-20121006-photogallery.html