That makes sense, but it didn't stop them in Crimea (back in 18whateveritwas). They chucked half a million soon to be dead bodies at it despite being technologically inferior and got skelped.
Vastly different demographic situation. Russia is now a much older country and has less young men to chuck at it. Plus it's generally the young Russians living in major cities that are most opposed to the war. Which is why their current invasion force has more ethnic minorities and folk from the economically struggling peripheries as they have less economic options and they tend to be younger than the population at large.