The graph legend says they don't show versions with user share lower than 0.1%, so one could infer that the user share for 2.1 is <0.1%, but they also say that this graph only shows "devices that visited the Google Play Store in the prior 7 days". Devices which haven't connected to Google's servers recently (for instance, because they don't have an Internet connection) aren't counted.
And while the development tools still allow developers to target older releases, there were large API changes in Android 3 and 4 (these were the versions which added tablet support), so developers often will target only API level 14 (Android 4) and above.
The graph legend says they don't show versions with user share lower than 0.1%, so one could infer that the user share for 2.1 is <0.1%, but they also say that this graph only shows "devices that visited the Google Play Store in the prior 7 days". Devices which haven't connected to Google's servers recently (for instance, because they don't have an Internet connection) aren't counted.
And while the development tools still allow developers to target older releases, there were large API changes in Android 3 and 4 (these were the versions which added tablet support), so developers often will target only API level 14 (Android 4) and above.