Aw not again. That stops me from trying so many android apps, since my phone only has 2.3 (officially that is).
I knew I'd be disappointing someone by going 4.0+. Honestly, it's high time to upgrade, but I could try making a separate build for 2.3, would take a bit of time to check which libraries work and switch the reader to use NineOldAndroids but it's possible. Not sure how well it would work and how far I can support that, though.
Also as mobile (game) developer myself, I can't help but wonder just what exactly stops so many from supporting 2.3 in abridged version at least. It might be gradually dying out, but it's still around 5% of devices.
That's because for games there is no reason not to support 2.3 as you're mostly just working with graphics that generally stay the same except for some extra GLES features available on newer devices. Most of the games I have do seem to support Gingerbread, I think.
But with native UI things have changed a lot. For example Gingerbread had basically no decent UI animation and even with third-party libraries it took a lot of effort to make things work properly. Hell, for certain animations I had to resort to change the layout parameters every frame - only because it just didn't work otherwise on some devices. Plus at this point many libraries don't play well with it so it just takes a lot of extra effort to make sure things work.
tl;dr generally because lazy or short on time