There are many possible explanations, so latching onto the first one that sounds plausible is not necessarily the correct one. Otherwise, we would all be like

There are many possible explanations, so latching onto the first one that sounds plausible is not necessarily the correct one. Otherwise, we would all be like those pundits on TV. Several reasons might also be simultaneously true. Some simple examples: Russia might be testing NATO. Russia might not want to escalate in certain ways. There have been many countries whose leaders want to minimize the numbers they kill, while still killing many people. Russia might not want to reveal otherwise unknown capabilities. They might be preparing their air to strike elsewhere, possibly unrelated to Ukraine. There might be a revolt inside Russia's military. And so forth. But, what's likely? Maybe they just don't want to kill everyone or create dissent.