Ultimately, they want a stronger foothold on the Black Sea, warm water ports and control of the Sea of Azov. Russia "annexed Crimea" giving them some of those

Ultimately, they want a stronger foothold on the Black Sea, warm water ports and control of the Sea of Azov. Russia "annexed Crimea" giving them some of those goals but they have only one way to reach it by land via a bridge and a long detour. Extending the "annexation" to the whole of south east Ukraine gives Russia two alternate land routes into Crimea and complete control over the Sea of Azov. In my personal opinion, the invasion/annexation/war was always about Mariupol and a unbroken land corridor across the northern coast of the Sea of Azov. Everything else is a smoke screen/distraction/false pretext.