The reason being that there's an effort to reduce the number of Humble Mobile Bundles being launched.
Until now, a new Mobile Bundle has rolled out every two weeks. This frequency has seen a noticeable drop in the quality of the bundles as of late ("meh" has been our general reaction).
Instead, mobile games will be distributed in other Humble Bundles more often.
This is what's happened with the recently launched "Made In Singapore" bundle, which contains two Android games.
There will still be Humble Mobile Bundles but these will be "special" ones. Hopefully that means the quality will return.