Why did Homo Erectus disappear?

"homo habilis died out because homo sapiens took over"

Actually, I'm pretty sure H. habilis went extinct between 1.6 and 1.4 million years ago whereas Homo sapiens originated about 200,000 years ago. It is possible that Homo ergaster could have driven Homo habilis to extinction, although probably not violently. More likely, it was a combination of multiple factors. I'd guess the usual culprits: climate change, scarcity of food due to Homo ergaster eating all of it...