I don’t think it’s break up, I think it’s resistance, they are getting stalled in the cities.
Ukraine has paved highways moving tanks isn’t an issue, except that the highways run through cities.
The problem is fundamentally that for every soldier and civilian they kill they are creating 5 to 10 freedom fighters. The more people are killed the greater the resistance. The less likely they can hold the country without reprisals from the people. If they have to resort to barbarism to subdue the people then the sanctions will never end.
Putin needs to establish a govt quickly that doesn’t have to resort to atrocities to govern. If he fails to do that he loses the greater overall war.