why would a basement collape if its in a x flood zone

X doesn't matter if you aren't handling water correctly, water always wins. Maybe they ignored cleaning gutters, downspout drain pipes or newly settled soil from removing trees that were beside the house...the roots take 10-20 years to rot away and can present deep holes or deep troughs. Maybe a yard swale finally filled-in with sediment, causing water to rush toward the house for some time. If you get rain, you have water to manage and keep away from the house as far as possible.