I don't think amaysim is targeting students and overseas...

I don't think amaysim is targeting students and overseas visitors. Their offer is about simplicity (BYO handset, no contract, unlimited (some deals), Australian based call centre) and can be attractive to anyone.
amaysim were one of the first if not the first operator in Australia offering sim only deals. Before that. Telco deals were based on monopoly money ($1,000 worth of calls for $100 and complex deals with a myriad of things included/excluded. since then the telco landscape has changed a lot and there are a lot of Sim only operators but amaysim was first in market and probably is still is the operator with the best customer service.