iOS with rare exception drops updates like a hot rock as soon as a new major version comes out. This is factually true:
The last security fix for iOS 1 was in July 2008, the same month iOS 2 came out.
The last security fix for iOS 2 was in January 2009, five months before iOS 3 came out.
The last security fix for iOS 3 was in August 2010, two months after iOS 4 came out.*
The last security fix for iOS 4 was in July 2011, three months before iOS 5 came out.
The last security fix for iOS 5 was in May 2012, four months before iOS 6 came out.
The last security fix for iOS 6 was in February 2014, five months after iOS 7 came out.*
The last security fix for iOS 7 was in June 2014, three months before iOS 8 came out.
The last security fix for iOS 8 was in August 2015, one month before iOS 9 came out.
The last security fix for iOS 9 was in August 2016, one month before iOS 10 came out.
The last security fix for iOS 10 was in July 2017, two months before iOS 11 came out.
* The two exceptions are a single update 2 months later, and a single update 5 months later.