There are 3 (R)easons why Singapore set a 99-year term limit on public housing and most private housing.
2 of which have been mentioned by the Singapore Government multiple times on multiple occasions.
The last reason was one we thought of as a potential reason that was not explained/explored by people.
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Reason One: Revitalise old Building(s)
Buildings deteriorate over time.
Eventually, there will come a time to demolish and rebuild.
However, if no absolute deadline is set, the probability of the building being demolished is ZERO as people living inside the building will not allow it to happen.
Hence a rule (or law in this case) has to be set in place to mandatorily allow the buildings to be vacated for demolishing and rebuilding.
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Reason Two: Re-purpose the Land...