larks

Indeed, but it is a bit hard to disable DST without some sort of "intervention" from the manufacturer. The code to change DST is already in the phone, at the time when you buy. And let's assume at a later time, a country decides to abandon DST. The code in your phone needs to be altered by the manufacturer to disable this. Which happens via updates

Most likely a software update should've arrived from your phone's OS vendor, to update the machanism that automatically changes the hour per a specific country/region. My guess is those phones that continued to switch to DST never got the update.