that's an incredibly short life - why demolished so soon?
I'd guess, because it became a problem social housing estate in a deprived area. Demolition of the whole estate was a real disgrace, considering that the less interesting James Stirling building, Branksome Conference Centre in Haslemere, Surrey is a Grade II* Listed Building.
The best of Southgate Estate Runcorn, the so called "Washing Machine" buildings, were unique and should have been restored, then Grade II* Listed, in my opinion.
Let us not forget that the Stirling Prize, the UK’s most prestigious architecture prize, was created in memory of James Stirling, who was the architect of many internationally renown buildings. Also, the architect of the Southgate, Runcorn Estate.
Below: James Stirling's Branksome Conference Centre in Haslemere, Surrey is a Grade II* Listed Building.