Be it local or foreign bride. It simply boils down to one thing. Two person get together because it improves their life.
If you have problem getting local girls, it is not because they are materialistic. It is simply because you cannot afford to give them the lifestyle they want.
The same thing applies to foreign brides. If they are staying in a kampong in their own country. Staying in a HDB in Singapore is simply a much better option for them. So they are willing to compromise and marry a much older man.
So end of the day, it is not really about sg women being materialistic. It is simply the fact that you are not able to give them a better lifestyle than they are having now. Nobody in the right frame of mind would want to downgrade their lifestyle be it girl or guy.