What is Russia waiting for? I think that is the most important questoin to be answered.
For fun we can speculate:
1. To me, the easy answer is they have motivation for a stalemate. Whether it be draining Ukraine and it's allies of resouorces or internally using a stalemate, politically, to motivate more investment in defense the stalemate can be a useful tool for Russia.
2. Ukraine has defensive positions that Russia is not yet comfortable overtaking or believe they can't. The Russians aren't hesitant to run paper through a shredder so I'm not sure how likely this is but something is giving pause.
3. The Ukraine theater in general is roo useful as a sharpening tool for the Russian armed forces. Early on in the conflict it was widely discussed how the US and Russians were sending moth balled equipment (cleaning out the closet), and in the russian's case, cleansing genetically and socially unfit citizens by sending them to the front. This seems like a reach, but plausible enough not to rule it out.
4. Does Russia want any more of Ukraine than it already occupies? Is it content with staus quo? This is an interesting question because noone really knows the answer. Putin has stated publicly that he would take Kiev, but taking any of his public statements at anything less than intimidation and manipulation tactics would be a mistake. He's not revealing **** in public other than what he wants us to think.
5. Is Russia running out of funding? Are the sanctions working? There are a lot of articles for both yay and nay when it comes to the sanctions effectiveness. Again, there is no link or article that is going to uncover the entire story. There may be elements of truth, but accurate economic data coming out of Russia is nonexistent.
6. Is Russia using the threat of invasion to influence political change in Ukraine. Parking his army on the banks of the Dnipro River anticipating the Ukrainian public losing it's appetite for war and demanding a political shift. This seems plausible, but Russia knows there many ways to influence regime change that doesn't involve the risks they are exposed to in Ukraine, so not likely.