Because Ukraine has drafted all their male citizens between the ages of 18 and 60 while Russia has largely limited their conscription to current military reservists or members of their military who were close to the end of their contracts. Until Putin conscripts all of Russia's male population, Ukraine's advantage is manpower. Russia's advantages are artillery and tanks.
This works because Ukrainians support the war. Many could have fled but have not. Many escorted their families out but then returned when they did not have to. Napoleon said that "Morale is to Material as Three is to One". And the Morale of the Russians in 2023 is clearly not the same as their morale in 1941, or 1812. Or to the morale of the Ukrainians in 2023. Not even close.
So Russia has needed to be more economical with their manpower than Ukraine. In order to defend Kherson, they moved thousands of troops from the north to the southern front. That left areas of Kharkiv inadequately defended so the Ukrainians took advantage of the gaps in Russia's defenses in the northern region.
Russia is not being economical with their troops at Bakhmut nor Soledar. They just want something to make a weak claim that they are making real progress.
Oh, by the way, since the Wagner Group announced that they have taken all of Soledar, they have bombarded Soledar another 93 times and counting.
3. The naval port of Sevastopol. Russia's Black Sea fleet is based there. (https://www.britannica.com/place/Sevastopol)
Doesn't matter. A fleet, like an army, has to be kept supply. Time magazine reported that if the land communications to Crimea are all cut off, the Russian fleet based there will have to sail to Georgia.
Crimea is a pipe dream for Ukraine. It's part of Russia for the forseeable future. I see no circumstance where Putin/Russia withdraws from Crimea.
We were told that Ukraine lasting a month once Russia attacked was a pipe dream. President Zelenskyy announced they must reclaim the Crimea before there can be peace. Zelenskyy has some street cred with me. Unlike those who hold that Russia must inevitably prevail, I think he knows what he is talking about. I think it can be done. Retired U. S. military officers think this can be done, so long as we maintain our supply of material and support. They think that if the thing is pressed, Ukraine will prevail. I say, in the words of Lincoln, "Let the thing be pressed".
I think the notion that Russia is going to magically turn things around, erase 30 years of mismanagement of their military at the snap of the fingers, is a pipe dream.