Ubuntu for Android tried to exploit full desktop PC potential out of multi-core Android phones. High-end Android phones could run Ubuntu when their Android phone was connected to a keyboard / mouse / monitor. Those not recalling this earlier Canonical endeavor can still see the Ubuntu for Android product page for at least the time being.
With Canonical now pushing heavily for their native Ubuntu for Phones/Tablets route, Ubuntu for Android (along with Ubuntu TV) have taken a back-seat. It's been confirmed earlier that Ubuntu for Android is no longer in active development. Canonical has now confirmed with Android Authority that no new Ubuntu for Android work is happening, at least until they have an interested launch partner.
Canonical still believes in the "U4A" product but they aren't in "concrete discussions with launch partners" and are focused on Ubuntu for Phones directly, which will also have a converged experience, and therefore aren't actively pushing Ubuntu for Android.