The relevant section of the article (in The Economist dated 28 January 2023) is below. 'Some' refers to 'The indoor leisure centres of the 1970s and 1980s'.
The indoor leisure centres of the 1970s and 1980s were about family and fun.
Their pools were curvy and fringed with trees. You walked into the
water via gently sloping beaches; the leisure centres’ architects had
discovered that many Britons could barely swim. They had wave machines
and waterslides, and some served alcohol. Their designers aimed to
bring the Mediterranean to ordinary Britons. As Britons took to
holidaying in the actual Mediterranean, some began to decline;
austerity and covid-19 finished them off.