This likely mirrors what happened when we moved from analog to digital. CDMA versions of phones like the Motorola v60 came with pull out antennas and were still capable of latching on to analog signals. It would drain the battery pretty quickly, but it worked.
Most people, most of the time, were riding digital signals and their phones never saw analog, but yet it was still there. A few things came into play:
1) The CDMA chipset in the phone had analog capability, so it was basically "free" to utilize.
2) Analog signal still worked well in rural/mountainous areas where it carried better.
3) It was still in active use with regional carriers they had roaming agreements with.
My guess is that similar conditions are why it is still in play in today's phones.
Most people, most of the time, were riding digital signals and their phones never saw analog, but yet it was still there. A few things came into play:
1) The CDMA chipset in the phone had analog capability, so it was basically "free" to utilize.
2) Analog signal still worked well in rural/mountainous areas where it carried better.
3) It was still in active use with regional carriers they had roaming agreements with.
My guess is that similar conditions are why it is still in play in today's phones.