Of course both sides have preconditions:
1) Russia: for Ukraine to accept territorial concessions (Donbas + Crimea)
2) Ukraine: for Russia to retreat from all Ukrainian territory, (maybe) except Crimea (meaning they're willing to sit down at a negotiation table without the Russians agreeing to retreat from Crimea)
So the two sides are far apart. Russia is judged weak because the prediction is that without negotiations they will lose all territory inside Ukraine. They are dependent on negotiations, and unwilling to accept the reality that they've lost the Donbas (Luhansk and Donetsk), Kherson, and Zaporizhia, and are unlikely to be able to hold Crimea in the long term.
Furthermore, Russia has consistently failed to demonstrate capabilities they threatened Ukraine with. They claimed to be able to take Ukraine "in 2 weeks, maybe less" (https://www.youtube.com/watch?v=h_RReQj7PpY), they claimed they couldn't be stopped in the Donbas. They have been stopped. They have been claiming for 40 years to have the tightest air defense network on the planet. The air defense network couldn't stop drones (which are unmanned planes, designed to fly slowly), not even with 6 WEEKS warning. They have panicked and deployed additional air defense platforms around Moscow, in other words, they're afraid they cannot protect the Kremlin from Ukraine's military, 450km from the nearest Ukrainian border whilst they cannot (effectively) hit Kiev's presidential palace, at 200km from their borders, and less than 70 from their deployed soldiers in Belarus. This is not the way to show strength.
They are known, even long before this conflict, to constantly lie about everything, to ignore agreements made before. So it's not even very clear what an agreement with Russia would even entail. If they say they won't attack, they can't be trusted to uphold the agreement. So what's the point? There must be a good military reason for them not to attack or there's no point.
Or to put it in negotiation parlance: BATNA for Ukraine is better than the conditions Putin demands to even talk. Nevertheless, these aren't small organizations: whether or not they've agreed to talk high-level, they're constantly talking.