The concept behind Loan Assessment Rates is to ensure you will be able to afford the loan repayments, in the future should interest rates rise.
Over the past number of years borrowers have had access to finance at what are historically low rates.
The low rates have meant borrowers have been able to borrow more than was the case a decade ago. (This access to historically cheap finance, has been one factor in driving up property prices).
Whilst we may continue to benefit from low rates in the near term, at some point they will rise. Which is why Lenders and APRA use Assessment Rates.