The amount of deposit required is controlled by the lender, guided by certain government regulations. Then they may add their own requirements on top of that. If they choose not do a 90% loan to non-PRs, that is their discretion. Best you can do is try another lender. Perhaps a mortgage broker could help you find a lender willing to work with you.
Bear in mind that the financial and housing markets are constantly changing. What was possible for "heaps of people" in the past may not be possible in the present; it may be possible again in the future. All you can do is choose the best option available to you now, or wait it out until something else comes up.