It has been more than five years since we said goodbye to the Android Market and hello to Google Play. You may have long since adjusted to the change, but there's been a version of the Android Market out there all this time. Google's putting an end to that soon, though. On June 30th 2017, the Android Market client on Android 2.1 and earlier will stop working.
The original Google Play rollout in 2012 included Android 2.2 and later. At that time, Eclair was already more than two years old. The Play Store client never came to those old devices, some of which apparently still exist. Anyone unlucky enough to be using an Eclair phone will soon lose access to apps in the Android Market. However, most of them won't work on Eclair anyway as developers have long since moved on.
There will be no warning about the shutdown on devices because of limitations in the Android Market client. It'll just stop working. Luckily, there aren't very many of these phones. Android 2.1 hasn't appeared on the monthly platform numbers in years, and that has a 0.1% threshold for inclusion.
- Android Developers