The last SFML release was just over 6 months ago, but the last one before that was 3 months.
This was all expected, even though one could've wished for it to happen even faster. SFML 2.1 was just a bugfix release, thus it fixed a few things that were either introduced with SFML 2.0, were discovered after SFML 2.0's release or small fixes. SFML 2.2 is a bigger step, especially with the mobile support.
Personally I'd probably made 2.2 yet another bugfix patch and now focused a bit more on getting as many issues resolved on GitHub, because the iOS and Android port are still rather unstable and need a lot more testing. And not to forget that Laurent, as the creator of the iOS port, as well as Jonathan, the creator of the Android port, don't seem to have too much time at their hands to actually help and motivate people to use/test the ports and fix all the issues asap. Just my thoughts...