I would say that the main factor was the economic depression before his time: Germany was especially affected because it also had to pay huge reparations for first world war.
This made people very desperate for change, and Hitler promised them this change: this is the reason why people wanted to choose him,
Further, I would argue that Hindenburg was very old at this time and no longer had the strength to oppose him,: this is a more direct reason why Hitler was made a chancellor at this time.
